I have tried to bold face all of the big words I had to use in the text, and define them when I first used them. This glossary may help if you encounter a term and the definition is not nearby.

Acetylcholine. A neurotransmitter that affects movement, learning, memory, and REM sleep.

Accommodation. What the eye does when we change our focus from near to far or back.

Action. Strides in which the horse lifts his feet high, flexing or bending knees and ankles.

Afferent. A nerve fiber that carries the signal of a sensory nerve from skin to spinal cord.

Aggression. A violent subset of agonistic behavior. The word labels hostile or violent behavior, and may include threats of such behavior, but excludes retreats, placation, and conciliation. Aggression is much more common in captive domestic horses than in feral horse bands.

Agonist. In neurochemistry, any chemical that binds to a receptor, activating it to produce some biological response. Testosterone is an agonist.

Agonistic behavior. A group of social behaviors that relate to fighting. Agonistic behavior may include warnings (threats and displays), efforts to break off an unpleasant encounter (retreats, placation), fighting, and conciliation.

Allen’s rule. The principle that an animal adapted for a cold climate will have a ratio of volume (which generates heat) to surface area (which loses heat).

Allogrooming Grooming another of your species. Many species engage in social grooming, including insects, birds, bats, primates, and ungulates (hoofed animals) such as cows and horses. Compare autogrooming.

Amble. Any 4 beat gait between a walk and a canter.

Altricial. Born helpless, and needing intensive parenting for the first period of life.

Amylase. An enzyme that converts starch to maltose

Autogrooming. Grooming yourself. Compare allogrooming.

Anger. Strong arousal state of both the sympathetic and parasympathetic branches of this system.

Antagonist. In neurochemistry, any chemical that blocks or dampens agonist-mediated responses. A blocker. Cortisol and serotonin may block the effects of testosterone, serving as antagonists. A dopamine antagonist is a substance that blocks the effects of dopamine.

Anthropocentrism. The notion that humans are the center of the universe, that plants and animals were put on the planet to serve us.

Anthropomorphism. An innate tendency to attribute human traits, emotions, and intentions to non-humans.

Appetitively motivated tasks. Tasks that involve approaching a reward or positive outcome.

Approximate Number System (ANS). A mental system that allows an animal to estimate the magnitude of a group without the use of language or symbols. Present in fish, birds, and mammals.

Asymmetrical gait. One in which the left and right side are not mirror images, such as the canter.

Autonomic nervous system (ANS). An unconscious control system found in all animals that regulates such things as heart rate, digestion, respiratory rate, and the fight-flight-freeze response. When triggered, the ANS quickly decides if we should fight, flee, or freeze. If fighting appears to be the best solution, the ANS triggers anger and aggressive behavior. If fleeing seems like a much better way to solve the problem, then flight is in order.

Availability Cascade. A self-reinforcing process in which a belief gains plausibility through increased repetition. Repeat something enough, and people come to believe it.1 We’ve seen this with “leadership” and “respect” in the world of horses. The bandwagon effect lies in wait as the cascade progresses: our tendency to believe what others believe. The bandwagon effect is behind the geographic distribution of saddle styles: western saddles are common in the south and west of the U.S., English in Great Britain and the northeastern part of the U.S., Australian saddles are common in Australia. So if everyone tells you that your horse doesn’t respect you, who are you to argue? The idea that “horses are prey animals” is an assertion that is an example of this effect.

Band. A family group of one adult stallion, one to three mares, and their foals.

Barnum (Forer) effect. Occurs when we believe fortune cookies, astrology, or personality tests to be accurate when they are applied to us or our horse, even if they are vague and general and would apply to many.

Basal meristem. The part at the top tip of the root of a plant such as grass.

Base rate neglect (Base rate fallacy). Names our tendency to ignore base rate information and focus on information from a single case. If you believe that riding bitless is OK for some but it is too dangerous for you, then you are ignoring the base rate of the tens of thousands who ride bitless without injury.

Beet pulp. The fibrous residue after sugar has been extracted from sugar beets.

Behavioral inhibition circuit. Triggers freezing if neither fight nor flight are possible. This is useful if you are a small mammal and a predator is close by: freeze and you might not be spotted. It may also be useful if you are a congressman, and fear predation by tweet. Activating the inhibition circuit has negative consequences, particularly if it is activated frequently. Frequent activation generates anxiety, ulcers, psychosomatic illnesses, hypertension, cancer… Compare punishment circuit and reward circuit.

Bias blind spot. Our notion that we are less biased than others.

Blind spot. The triangular area between the eyes and extending forward, in which an animal is not able to see. Horses have a much larger blind spot than humans.

Bolus. A small rounded blob of warm grass and saliva, suitable for swallowing. You go first.

Bonding. The development of a close attachment between romantic partners or close friends or between parent and child or between you and your horse.

Bosal-Style Hackamore. A hackamore with a noseband with a “bosal” (knot or button at the bottom), and the pressure on the nose is what gets the horse’s attention and turns it or stops it. The reins are a single length of soft rope (a “mecate”), tied to define the size of the bosal. The looped reins may be tied to any length, and leave an extra length, so that when untied, they serve as a long lead rope. The noseband is typically made of stiff rawhide.

Breaking. Preparing a horse to be ridden. In traditional horsemanship, this involves breaking his spirit, and creating a feeling of learned helplessness.

Breeding dispersal. Dispersal of adults after the breeding season, preventing inbreeding. Cf. natal (or juvenile) dispersal.

Cause. This is the specific force that made something happen. It could be the release of oxytocin or ethylene. It need not be understood, and the effect need not always occur every time the cause appears. (cf reason)

Cold-Blooded: Heavier, shorter build than a warm or hot blood. The extremities (tail, ears, limbs) are relatively short. The skin is thick and conceals the blood vessels, there are substantial subcutaneous fat deposits which are readily built up or mobilized as the need arises. Calm and very sociable. While not capable of sudden effort, it has high endurance capacity, i.e. it can sustain low-powered effort for long periods. It has very considerable aerobic capacity and is apt to mobilize its body reserves for muscular effort.2 Examples: Belgian, Clydesdale, Percheron, Shire.

Colic. Abdominal pain.

Collective decision making. The process by which a herd, school, flock, or other group of animals makes a decision to do something. This works just fine without a leader.

Confirmation bias. Our tendency to search for and focus on information that agrees with our initial views. Explains why some watch Fox News but not MSNBC, and others reverse this pattern. This bias might underly your putting this book down before you finish it, but my hope is that you won’t put it down. Keep reading and you’ll surely find something you agree with. You will show a continued influence effect if you continue to believe what you now believe after you’ve been exposed to “alternative facts.”

Conservative belief revision. Describes what we do when we discover that what we believe is wrong: we change our belief less than the amount that the new information demands.

Conserved. When a quality is conserved, it is found in a species as well as some distant ancestor, and all those in between. A behavior like moving away from trouble or moving toward food or scratching an itch goes back to the first movement. Find a behavior in several related species, and it is likely that their common ancestor did this. Such similarities are called homologies. Similarities not due to a common origin are called homoplasies.

Contralateral dominance. The fact that each of the brain’s hemispheres is best focused on input from the other side. The left side of the horse’s brain handles the bulk of input from his right eye and right ear, and vice versa. Accompanied by specialization of the hemispheres, this may have consequences for how a horse reacts to a sight or sound coming from one side.

Coevolution. When two closely associated species influence each others’ evolutionary development, as with milkweed and monarch butterflies, or dogs and people.

Cold-Blooded. A horse that is heavier, shorter build in general with a high compactness index (chest circumference/height at withers). The extremities (tail, ears, limbs) are relatively short and are protected by hair, mane and fetlock. The skin is thick and conceals the blood vessels, there are substantial subcutaneous fat deposits which are readily built up or mobilized as the need arises. The animal is calm and very sociable with its fellows. While not capable of sudden effort, it has high endurance capacity, i.e. it can sustain low-powered effort for long periods. It has very considerable aerobic capacity and is apt to mobilize its body reserves for muscular effort. Examples: Belgian, Clydesdale, Percheron, Shire. Compare Warm-Blooded.

Colt. Immature male horse. cf filly.

Cones. Better than rods for detecting details of an image. Can detect color. The cones in our eyes work best in bright light, give us the details of an image, but are not as good as the rods at detecting small differences in contrast. In humans, there are three types of cones, which detect red, green, or blue. Horses have only two types of cones, which detect blue or green, but not red. The colors seen by horses are the basic plan for most mammals that can see colors.

Contrafreeloading. A voluntary behavior in which an animal choose to work for food, rather than eat what is provided.

Cortisol. Gives a feeling of anxiety, interferes with sleep, and its level rises when we feel danger or stress. I suspect that its rise is triggered by the situation, and causes those feelings of danger or stress. When the cortisol level goes down, we feel good. I suspect it is released when a horse is separated from his herd, or when any social animal is separated from others. When an animal loses in combat for status in a group, its cortisol level goes up, and remains up, while the winner’s cortisol level drops. Massage has been shown to decrease cortisol levels. Facilitates prefrontal area cognitive control on impulsive tendencies aroused in the subcortical structures. An antagonist for testosterone.

Counter-canter. A canter on the wrong lead.

Cribbing. An oral behavior in which the horse grasps a surface with his incisors, arches his neck, contracts the lower neck muscles to retract the larynx. As the horse does this, air rushes into the esophagus making a grunting sound.

Cutaneous trunci muscle reflex. The reflexive twitch of muscles just beneath the skin of a horse. Occurs when flies land and other light touches occur.

Dead reckoning. A process in which we constantly update our sense of the distance and direction of some place, without regard to the route we have taken.

Diagonal gait. A gait in which the front foot and diagonally opposite hind foot take off and land at the same time. The trot is an example of this gait.

Diastolic blood pressure. The pressure in the blood vessels when the heart is resting between beats.

Digesta. Ingested food in the process of being digested.

Dogma. A set of principles and beliefs that are accepted without being questioned.

Domestication phenotype. The appearance of an animal which has been domesticated.

Dominance hierarchy. A social structure that has developed through a series of conflicts between pairs of individuals, in which one established a higher rank than the other.

Dopamine. A neurotransmitter that controls movement and posture, modulates mood, and plays an important role in both positive reinforcement and dependency. The brain contains several dopamine pathways which are involved when we are motivated by a reward, when we meet a goal, or when drugs or alcohol make us feel intoxicated. Dopamine underlies both addiction and the effectiveness of positive reinforcement. Operating in the reward circuit, dopamine is released to produce pleasure — a global reward signal. Dopamine works as a local chemical messenger outside the central nervous system. Blood vessels, the kidneys, the pancreas, and the immune system all produce dopamine, with effects ranging from increasing urine output in the kidneys, reducing insulin production in the pancreas, and increasing vasodilation in blood vessels.

Electrolytes. Produce an electrically conducting solution when dissolved in water, and are critical to the operation of nerves and muscles. Examples include sodium, potassium, calcium, bicarbonate, magnesium, chloride, and hydrogen phosphate.

Emotion. Like mood, but not completely accounted for by biology — they also have a cognitive layer that provides them with a context, an explanation, a rationale. And they have behavioral and subjective components, too. Emotions are likely to accompany a mood. Emotions often have an object: When you feel jealousy, you are jealous of someone. When you are annoyed, you are annoyed by something or someone. Also see mood.

Endorphins. Endogenous morphine — are a morphine-like substance that the body produces. The are “endogenous opioid neuropeptides” found in the neurons of both the central and peripheral nervous system. Endogenous simply means that they are produced by the body. Opioid means that they are opiate-like, acting on opioid receptors to produce morphine-like effects. A peptide is a protein-like molecule made from two or more bonded amino acids. Neuropeptides are neurotransmitters produced and secreted by nerves and used for signaling other nerves. Endorphins are likely involved in analgesia (pain reduction), reinforcement, cognitive function and motor integration. Released when we are stressed, fearful, or in pain. Masks pain by binding to opioid receptors and activating them, inhibiting pain signals. Responsible for the euphoria of a runner’s high. May also be stimulated by laughter. Heroin, morphine, and marijuana mimic the effect of endorphins. Scents such as vanilla and lavender trigger endorphin release. Laughing, listening to music, eating chocolate, having sex, and taking a group exercise class may all release endorphins. Massage has also been shown to increase endorphin levels.

Environmental enrichment. The improvement of enclosure design, and the use of feeding devices, novel objects, and appropriate social groupings to stimulate captive animals.

Epidermal growth factor (EGF) . A growth factor that stimulates cell growth, proliferation, and differentiation.

Epinephrine. A hormone and neurotransmitter (and medication) that affects metabolism of glucose and energy release during exercise.

Erogenous zone. An area of the body that is more sensitive to touch than other areas.

Estrogen. This hormone has three important effects on a mare’s courtship. It increases her willingness to approach a male and induces solicitous behaviors. It improves the mare’s attractiveness to a stallion either directly or through the production of odors, pheromones, and vocalizations. And it primes for progesterone.

Estrus. In heat. A brief period of sexual receptivity in which a mare is fertile.

Evaporative cooling. Cooling that occurs because liquid (such as sweat) evaporates from the surface.

Extinction. The disappearance of a previously learned behavior when reinforcement stops.

Face validity. When a procedure or measurement appears to be an appropriate and representative of some desired state outside the experiment.

Fear. High arousal of the sympathetic branch of the autonomic nervous system. See also anger.

Fecal midden (stud pile). A pile of poop created by one or more stallions during breeding season. Stallions add to it again and again.

Feral. Living in the wild, but descended from domesticated animals. The mustangs in the American West are feral, not wild.

Filial imprinting. This is the following reaction which develops in precocial birds just after birth, in which they follow the first moving animal that they get close to — usually their mother. See also sexual imprinting, imprinting.

Filly. Immature female horse. cf colt. ;

Flehmen response. The Flehmen response is a very noticeable facial expression, but it only means that a fascinating scent has been detected, and the horse is using his vomeronasal gland to learn more about it. When a horse shows the flehmen response, it curls its upper lip, inhales, and draws substances into its Vomeronasal organ.

Flying lead change. Switching from one lead to the other without breaking gait, during the suspension phase of the canter.

Foal. Horse or pony of either sex under one year old. cf colt, filly, weanling.

Foregut. Esophogus, stomach, and small intestine.

Friendship. A preferential association between two individuals, wherein each is more likely to choose the other to associate with than other parties. This association implies that each obtains some benefit from the other, and that each is likely to refrain from harming the other.

GABA. The chief inhibitory neurotransmitter. It reduces neuronal activity and helps regulate muscle tone.

Gait. Refers to a cycle of limb actions that an animal uses repeatedly when moving.

Gelding. Castrated adult male.

Grazer. Grass eater.

Glutamate. A neurotransmitter active in areas of the brain involved in learning, thought and emotion. It is abundant in the body, and is used in over 90% of synaptic connections to the brain.

Google Scholar. Greatest thing since sliced bread, and the life force in writing this book. Want to find what science has learned about a topic? Go to

Habituation. The diminishing of a physiological or emotional response through repeated exposure.

Harem tending. The stallion business of recruiting a harem and hanging on to the gals once they are recruited.

Hemispheric lateralization. Specialization in the brain, in which one side or the other has dominance in certain kinds of processing.

Herd. A group of horses. May consist of multiple bands.

Herd bound. Any horse who is very closely attached to one or more friends in his herd, and is reluctant to leave them.

Herding. The efforts of a feral stallion to drive his mares from one place to another.

Hindgut. The cecum and colons.

Homologies. Characteristics sharing a common ancestry.

Homoplasies. Characteristics sharing a common function but not a common ancestry.

Hormone. A chemical messenger that is produced by the adrenal glands and released into the blood stream. Their signaling is done by chemical impulses. They carry information through the body more slowly than neurotransmitters, but their effects can last longer. A single chemical compound — such as epinephrine, oxytocin, and vasopressin — can be used both as a neurotransmitter and a hormone.

Horse. Equus caballus greater than 14.2 hands (145 cm) at the withers (shoulders).

Hot-Blooded. Hot blooded horses fit the description for warm bloods, but do better in even hotter circumstances. They will need more blanketing than Cold Bloods or Warm Bloods. There are only two recognized hot-blood breeds: the Arabian and the Thoroughbred.

Hypernatremia (salt poisoning). Occurs when a body takes in dangerously high levels of sodium. Too much sodium in the bloodstream can cause trouble breathing, damage kidneys, trigger nausea, vomiting and weakness, damage brain cells, and lead to seizures, coma or even death.

Hypertonicity. When the ratio of salt and fluid in the body is higher than normal.

Hyponatremia. Occurs when a body’s sodium falls dangerously low. Symptoms include a decreased ability to think, headaches, nausea, and poor balance. Severe symptoms include confusion, seizures, and coma.

Hypotonic dehydration. Occurs when there is some water loss and a considerable loss of electrolytes during dehydration. Compare isotonic dehydration.

Illusion of control. When you overestimate the extent to which you control a situation.

Imprinting. The process in which a very young animal bonds with some other animal or thing. The term was first used to describe chicks who, at birth, quickly learned to follow their mothers on land and in the water. Scientists don’t use the term “imprinting” when discussing mammals because mammals don’t imprint the way birds do. Takes at least two forms: filial imprinting and sexual imprinting.

In-group bias. Favoring members of the group you belong to. In the pasture, a newly added horse is not yet in the in-group, and won’t feel welcome. In your barn, riders may be nested into several groups. Inside the group, bonds grow, and between groups bonds weaken. Oxytocin may underlie part of this phenomenon.

Instinct. An unlearned fixed action patten that is triggered by some stimulus.

Interspecies. Between members of two different species.

Intraspecies. Between members of the same species.

Introgression. Repeated backcrossing. In breeding, crossing progeny with parent.

Isotonic dehydration. Occurs when there is water loss and electrolyte loss correspond to their normal levels in the blood. Compare hypotonic dehydration.

Jumping cavesson (Jumping hackamore). A hackamore with a leather noseband and side rings for the reins. The noseband is often leather wrapped cable. It is essentially a sidepull hackamore that is more closely fitting. Compared to a sidepull hackamore, it offers less lateral control and more stopping control.

Latherin. The thick foamy stuff on a sweating horse. It acts as a surfactant to get horse’s hair wetter, providing more surface area for sweat to evaporate from.

Law of Parsimony (Occam’s Razor). States that among competing explanations, the one with the fewest assumptions should be selected. The simplest explanation is not necessarily more likely to be right, but it is more easily tested and more easily remembered. Often the simple explanation covers more cases than an explanation with many clauses and caveats.

Lead. At a canter or gallop, the lead refers to which rear foot reaches farther forward. When moving around a track on the correct lead, the inside front and rear legs reach farther forward.

Learned helplessness. A condition in which an animal feels a sense of powerlessness, having learned that he it has no control over its environment, no means of avoiding pain. Learned helplessness is created by breaking, and is commonly found in lesson horses.

Left hemisphere. Left side of the brain. In the horse, it processes positive emotions, such as pleasure from eating, is specialized for approach, produces vocal communications, recognizes species-specific vocalizations, categorizes stimuli, controls responses that require choices, inhibits responses until decisions have been made. In the horse, what is seen through the right eye is the primary visual information processed here.

Left lead canter. A 3 gait sequence in which the left hind leads the right hind. Left rear and right fore move together. The left fore lands in front of the right fore.

Listening vocabulary. The set of words that we know when we hear them spoken.

Long-day breeder. An animal that breeds when days are lengthening — in the spring.

Low-forage diet. A diet in which a high proportion of intake is from concentrates and grain, and a smaller proportion from hay.

Magic. The notion that the connection between cause and affect can occur through supernatural forces.

Mare. Intact adult female horse.

Matriarchal Society. Girls rule — in most species of mammals.

Mechanical Hackamore. A hackamore with long metal shanks and a curb chain that runs under the jaw. They offer great stopping power with their leverage, but are not very effective with lateral control.

Mechanoreceptor. A nerve that can sense touch.

Meissner (tactile) corpuscles. Stack of flattened disks in the dermis just below the epidermis. Encapsulated in an envelope of connective tissue. Respond to light touch. Respond only at the onset and offset of stimulation. In humans, they are concentrated in thick hairless skin, such as the finger pads and lips. Do not detect pain. Put on a hat, and your Meissner corpuscles will notice. Wear it a few minutes and they’ll stop firing, so you’ll forget it is on. The density of these corpuscles diminishes with age, until we reach the state of no sense, no feeling.

Merkel corpuscles. Disk-shaped receptor formed by a Merkel cell and a free nerve ending. Located in the basal epidermis (deepest layer of skin) and hair follicles. Not encapsulated in connective tissue. In humans, found most often in sensitive finger tips, and handy for reading Braille. Respond slowly, but may fire for more than half an hour if stimulation continues. Up to 90 such nerve endings are handled by a single afferent nerve fiber. Store neuropeptides such as dopamine and serotonin which they release to associated nerve endings in response to pressure. Used for tactile discrimination, responding to gentle localized pressure, to feel a detailed surface. Massaging your horse will stimulate these nerves in your finger tips and on his skin where you are rubbing, releasing dopamine, serotonin and other wonders.

Midas effect. When touch doesn’t produce gold, but produces recipients with more positive emotions and goodwill toward others.

Mood. A background state that is less specific than emotions, and that has a biological counterpart. Moods differ in valence (positive/negative) and strength (mild/intense), but don’t have any “cognitive” component. They are states that influence how we feel, but don’t direct specific action toward any target. Moods may not be immediately noticed by the one experiencing them. They may last longer than emotions. They may be less intense than emotions. They are usually not triggered by any specific thing or event. Some moods: anxious, calm, contented, depressed, excited, fearful, happy, relaxed, sad. Also see emotion.

Motor laterality. Sidedness or handedness in motor function.

Mugging. A horse behavior in which it searches for food on a handler. The behavior is inadvertently produced by handlers through operant conditioning, and may be eliminated through operant conditioning.

Mundane realism. The similarity of the conditions of an experiment to the horse’s real world and normal day.

Mutualism. A symbiosis in which two species benefit each other. Key to the evolution of both humans and dogs.

Natal (or juvenile) dispersal. Dispersal of the youngsters out of the breeding territory. Prevents inbreeding. Cf Breeding dispersal.

Natural horsemanship is a term used to describe a variety of horse training techniques that are believed to be less abusive than traditional techniques, while still achieving the desired level of control over the horse.

Near fore. the horse’s left front leg.

Near hind. the horse’s left rear leg.

Nearside. the horse’s left side.

Neoteny. The retention of juvenile characteristics into adulthood.   Humans and dogs may both have experienced neoteny in their evolution.

Negative punishment: taking away a pleasant stimulus. Your cell phone rings, and you stop grooming to answer the call.

Negative reinforcement (NR): taking away an unpleasant stimulus. You relax the reins, releasing pressure on the bit. NR occurs during behavior, and ends with a change in behavior. A horse learns to behave differently with NR if it ends the exact moment that the undesirable behavior ends. For instance, suppose you want your horse to move toward you on some cue. You give him a little tap with your whip, he moves toward you, and you stop tapping. This sequence is that of NR.

Neuropeptide. A compound that acts as neurotransmitter, sending signals between nerve cells or between nerves and other cells.

Neuropsychology. Studies how the nervous system and brain underly behavior, emotion, and cognition. Neuropsychology builds on an understanding of neurotransmitters and their effects.

Neurotransmitters. Chemical messengers that bind two nerves at a junction called the synapse. The presynaptic neuron contains vesicles — small spherical chambers — containing various neurotransmitters. These neurotransmitters — sometimes called hormones — are secreted into the synaptic gap when the first nerve fires. Once released, they close the gap and bind to membrane receptors in the adjoining postsynaptic neuron.

Nociceptor. A sensory neural receptor that signals when it senses potentially damaging stimuli. Some nociceptors respond to noxious heat or cold, some respond to pressure or cuts that break the skin surface, and some respond to chemicals. Nociception evokes a reflex that moves the entire animal, or at least the affected part, away from the noxious stimulus. Nociceptors have been found in leeches, nematode worms, sea slugs, molluscs, fruit flies, birds, horses and other mammals, human embryos, and — sufferin’ catfish — in fish.

Nonspecific erogenous zones. Areas of heightened sensitivity which contain a higher density of mechanosensory nerves. When these zones are stimulated, they produce pleasurable feelings, though not the same heightened sexual arousal that is produced by specific zones. Nonspecific zones in humans include the sides and back of the neck, the inner arms, the armpits, and the sides of the chest.

Norepinephrine. A neurotransmitter that affects eating, alertness, and wakefulness, and mobilizes the body for action.

Not invented here. Neophobia: an aversion to new stuff. My guess is that you wouldn’t want to try a Mongolian saddle, bridle, or bit — even though the Mongols conquered the known world with this stuff.

Occam’s Razor. See Law of Parsimony.

Off fore. the horse’s right front leg.

Off hind. the horse’s right rear leg.

Operational definition. A definition that comes from measurable behavior.

Overdetermination The presence of two or more sufficient causes.

Oxytocin. A neuropeptide and a peptide hormone. As a neurotransmitter, it is created in a nerve cell. As a hormone, it is created in the hypothalamus and released by the pituitary.Gives a feeling of friendship, love, deep trust. Its effects last longer than those of dopamine. Oxytocin likely contributes to a mare’s love of her foal, your fondness of your horse, and your horse’s fondness of you. Oxytocin is produced in the hypothalamus and released by the pituitary. It is released during bonding, kissing, hugging, sexual reproduction, both during and after giving birth, and during nursing.

Pace. A symmetrical lateral two beat gait in which both legs lift off from one side, then the other.

Pacini (Lamellar or Pacinian) corpuscles. Encapsulated in an envelope of connective tissue. Respond rapidly, but only at the onset and offset of stimulation. Respond only to sudden disturbances. Used to detect vibration and sudden gross pressure changes, such as a hard poke. When a spur touches a horse’s flank, it is Pacini corpuscles that first respond. When the spur is removed from the flank, it is Pacini corpuscles that first respond. Continuous pressure does not get these corpuscles to fire, but they do respond in a graded way to pressure: the greater the pressure, the stronger the signal they send.

Pain. I use this term as if it always implied suffering, without concern for the degree of consciousness the animal is experiencing. I believe that any species that is capable of motion is likely capable of making an effort to avoid injury, and thus is likely capable of experiencing pain and suffering. Pain is a fundamental of learning, of adapting, and of survival of both an individual and a species. Pain is not good. It hurts. But pain is useful: it is a quick teacher. Also see pleasure.

Paradoxical Sleep. Another term for activated sleep, deep sleep, desynchronized sleep, rapid eye-movement or REM sleep, para sleep, and rhombencephalic sleep. Since dreaming occurs almost exclusively during this sleep state, it is also called dreaming sleep or D-state. Compare Slow Wave Sleep.

Parallel evolution. Evolution in which one selection pressure had similar effects on two species.

Paternal skew. One stallion gets dates with more than one mare. Benefits from estrus synchronization.

Pheromone. A chemical messenger that carries information between individuals of the same species. In the horse, pheromones are detected by the vomeronasal organ and processed in the amygdala.

Pinnae. The external ears of a horse or mule or other animal. (singular: pinna)

Pirouette. A swivel around the hindquarters, the forehand moving in a large circle and the back in a very small circle.

Pleasure. A fundamental of learning, of adapting, and of survival of both an individual and a species. Pleasure is good. It feels good. And pleasure is useful: it is a quick teacher. Also see pain.

Pollyanna Principle (also optimism bias, wishful thinking and positive outcome bias). A tendency we all have to learn positive stuff better, remember it better, and emphasize it in our lives. We like to see no evil, hear no evil, and say no evil. I wrote a book on this3.

Pony. Equus caballus less than 14.2 hands (145 cm) at the withers.

Positive cognitive bias. A bias toward positive events. We are more attentive to them, learn them more easily, memorize them better, and expect them more often.

Positive punishment: receiving an unpleasant or aversive stimulus. Your horse receives a yank on the bit. In everyday language, this is usually what we call “punishment”.

Positive reinforcement (PR): receiving a pleasant stimulus. Your horse gets a treat or praise. In everyday language, this is usually what we call “reward”.

Post-purchase rationalization (choice-supportive bias). A cognitive bias in which we retroactively ascribe additional positive attributes to whatever we have chosen. It will increase your liking of this book if you paid for it. And if you paid a lot, you’ll like it more than if you paid very little. This rationalization will help you feel better about dumb purchase mistakes. That unrideable horse that you paid $20,000 for? A good investment after a little more training.

Precocial. Born in a developed state, and able to move within a short time after birth. Cf. altricial.

Preyer’s reflex. Immediately pointing one or both ears in the direction of a new sound.

Progesterone. This hormone has a dual affect on courtship. When it is on the rise after priming by estrogen, the mare’s sexual receptivity increases. But the prolonged secretion of progesterone inhibits sexual receptivity and helps maintain pregnancy.

Przewalski’s horse. Equus ferus przewalskii or Equus przewalskii and pronounced shuh-VAL-skee The only species of truly wild horse left in the world. They became extinct in the wild in 1969, survived through careful captive breeding, and have since been introduced.

Punishment occurs after behavior and makes that behavior less likely. In contrast, if you were to ask your horse to move toward you, and he did not, and you then punched him in the face for being so disobedient, he would learn to fear you, learn to distrust you, learn to stay away from you. He would not learn to come to you when you asked.

Punishment circuit. Involves a sequence of detecting danger then fleeing — or if that is not possible — then fighting. Fight is triggered if flight is not possible. Both fight and flight may lead to satisfaction if they are successful. Compare reward circuit and behavioral inhibition circuit.

Quidding. A response to mouth pain in which the horse loses or spits balls of semi-chewed food stuffs out of their mouth.

Rapid Eye Movement (REM). The movement of the eye during a dream. In insects, the equivalent is likely rapid antennal movement during dreaming. And in a big saltwater snail I know, there seems to be simply undirected chewing while everything else signifies he is sleeping: eyes retracted, head immobile, and body positioned in his sleeping position: at the bottom of the tank, shell resting on the sand, with his foot against the glass.

Reactive. Showing fearfulness and avoidance where other horses remain calm and approach a handler.

Reason. An explanation for why something happened. (cf cause) Reasons often assume too much, or don’t include a motivational component. Some reasons trick us because they simply re-label something.

Rebound effect: When a horse is deprived of such a behavior and then finds itself in a situation where it can perform the behavior, the behavior returns — sometimes with more vigor than just prior to deprivation.

Recruitment. The process in which one animal such as a horse gets another horse to follow him.

Reification. The process of turning an idea into a fact. Treating something as material when it is immaterial.

Reinforcer. Anything that occurs after a behavior which makes that behavior more likely.

Respect. a feeling of admiration or deference, a feeling of regard for the qualities of the one respected.

Reward circuit. Consists of a sequence of desire, action, and satisfaction. This dopamine pathway is central to reward-motivated behavior. Approach, pleasure, and learning are all managed by this circuit. Compare punishment circuit and behavioral inhibition circuit.

Riding Halter. A halter designed to keep the cheek pieces away from the horse’s eyes, does not interfere with jaw motions like a bitless bridle can, and is intended for maximum comfort of the horse. It is worn with a loose nose band, maximizing the horse’s comfort. It offers limited lateral and stopping control.

Right hemisphere. Right side of the brain. In the horse, it processes negative emotions such as fear and aggression, is specialized for attack or avoidance, processes vocal communications of modulated frequency, transmitting information about the identity of the emitter, whether a threat is present, and details about the threat. It is specialized for quick reactions to novel stimuli. Neophobia lives here. In the horse, what is seen through the left eye is the primary visual information processed here.

Right lead canter. A 3 gait sequence in which the right hind leads the left hind. Right rear and left fore move together. The right fore lands in front of the left fore.

Rods. The rods in our eyes formed the earliest basis of vision in vertebrates. Rods are best for seeing in very low light, or for sensing differences in light level. But they don’t work as well as cones for detecting details of an image, and can’t detect color.

Rollkur. Hyperflexion of the horse’s neck achieved through aggressive force.

Ruffini’s (Ruffii or Bulbous) corpuscles (Ruffini cylinder). An onion-shaped structure enclosed in an envelope of connective tissue deep within the skin and in joints. Respond slowly and continuously for the duration of stimulation. Responsible for kinesthetic control and movement. Respond to stretch and torque of skin and tendons. In humans, they are at their highest density around the fingernails, and may help detect whether an object we are holding is slipping from our grasp. Horses find these useful in grasping grass.

Sci-Hub. Once you have found a scholarly reference with Google Scholar, you can likely read it at (The URL may have changed by the time you read this, because companies like Elsevier are trying to take this site down.) Sci-Hub is becoming the world’s single biggest library of scientific articles.

Sentience. The capacity to feel, perceive, or experience subjectively. Any species that can suffer, can feel pain, is sentient.

Serotonin. Serotonin is a neurotransmitter found in the gastrointestinal tract, in blood platelets, and throughout the central nervous system of all animals. Serotonin gives humans feelings of pride, of well-being, of happiness, and of being loved. Serotonin can affect mood, social behavior, appetite, digestion, sleep, learning, memory, and sexual desire. Imbalances in serotonin can result in depression, suicide, impulsive behavior, and aggressiveness. Drugs like LSD, PCP, and Ecstasy mimic the effects of serotonin. Serotonin is found in all animals. In insects, it has roles similar to those it has in humans, affecting memory, appetite, sleep, and behavior. When serotonin levels in locusts rise, they transform from a solitary life to a gregarious state. Serotonin is not limited to animals. Serotonin derivatives have been found in at least 16 different plant species. These derivatives help plants defend against pathogens and provide them with therapeutic benefits.

Sexual imprinting. In birds, the attraction to a mate of the same species as that which the chick imprinted on — usually the parent.

Short-day breeder. An animal that breeds when days are growing shorter — in the fall.

Sidepull Hackamore. A hackamore with a noseband, usually of rope, rawhide or heavy leather, with reins that attach at the cheekpieces. It offers significant lateral control but limited stopping control.

Simple change. Changing leads while not changing gait, at walk or trot.

Skin turgor. The skin’s propensity to rapidly return to its normal contour after being raised in a fold pinched between an examiner’s thumb and forefinger.

Slow Wave Sleep (SWS). During SWS, brain waves are slow and regular, and the horse is not dreaming. A horse can engage in SWS both standing and in the sternal recumbent position. In this state, the horse’s head is down, and his lower lip has relaxed. Eye movement is diminished, and the eyelids may be open a bit. There is usually a small amount of muscular activity, and while the horse’s vigilance is reduced, the horse can still respond quickly to disturbing sounds or smells. Compare Paradoxical Sleep.

Social neuroscience. An interdisciplinary field devoted to understanding how biological systems implement social processes and behavior, and to improving theories of social processes and behavior.

Stallion. Intact adult male horse.

Status-quo bias. Advises us “If it ain’t broke, don’t fix it.” We like to “stick to our guns” because we fear that anything different will likely be worse. Behind the hankering for the good old days.

Stereotypy. Persistent repetition of some behavior, without evident purpose. Often seems to be a result of prolonged confinement, or isolation. Pacing, cribbing, weaving, and self-mutilation are examples.

Stride. The distance covered by a horse’s foot, measured from first imprint to second imprint of a horse’s foot.

Sympathetic nervous system. Sometimes called the “fight or flight”, “quick response”, or “mobilizing” system. A branch of the autonomic nervous system. Compare parasympathetic nervous system.

Synapse. A junction between two nerve cells, consisting of a tiny gap. Impulses from one nerve are sent across the gap by diffusion of a neurotransmitter.

Tapetum lucidum. A pigmented part of the eye which reflects light back onto the retina, allowing for greater absorption when it is dark.

Tending. A stallion’s following of a female who is approaching estrus. It is herding without the directional drive.

Testosterone. A naturally occurring steroid hormone. Found in both males and females, it is the primary male sex hormone, promoting secondary sexual characteristics such as more muscle, larger bones, and more body hair. It exerts its action through binding to and activation of the androgen receptor. Testosterone activates the subcortical areas of the brain to produce aggression. Antagonists: cortisol and serotonin.

Theory of mind. The ability to attribute mental states—beliefs, intents, desires, pretending, knowledge, etc.—to oneself and others and to understand that others have beliefs, desires, intentions, and perspectives that are different from one’s own.

Time budget. For a horse, an exhaustive accounting of what horses do during the course of a day (or other interval).

Tonic immobility (thanatosis). Freezing, rather than fighting or fleeing, when death seems certain. May occur with some prey when they are seized by a predator.

Track up. a hind hoof lands in the hoof print of the front hoof of the same side, or ahead of that print.

Traditional horsemanship emphasizes efficiency over kindness, and sets out to break a horse’s spirit and develop learned helplessness through domination and pain. Traditional horsemanship usually works well to develop a passive, compliant horse in a short period of time. The emphasis is on making the horse useful rather than happy, on having control rather than companionship, and on coercion rather than cooperation.

Transitive (linear) hierarchy. If A dominates B, and B dominates C, then A dominates C. This is an example of the “transitive property of inequalities.” But intransitive (non-linear) hierarchies (A dominates B, B dominates C, and C dominates A) happen in large herds, especially near the bottom of the hierarchy.

Two-choice preference test. An experiment in which a horse or other animal is provided with two choices — a pair of buckets in his stall or some activity at the end of each arm of a Y-maze — and allowed free choice. Observations may be of speed of choice, frequency of choice, etc.

Vasopressin. A hormone found in most mammals. It normally contains arginine, and is sometimes called arginine vasopressin. Most of vasopressin is stored in the pituitary before it is released into the bloodstream. However, some vasopressin may also be released directly into the brain, and accumulating evidence suggests it plays an important role in social behavior, sexual motivation and pair bonding, and maternal responses to stress.

Visual streak. A linear area of the retina with a high concentration of ganglion cells. Functionally equivalent to a fovea.

Volatile organic compounds (VOCs). Organic compounds that easily vaporize. Besides carbon, they contain elements such as hydrogen, oxygen, fluorine, chlorine, bromine, sulfur or nitrogen

Vomeronasal organ, VNO or Jacobson’s organ. Senses large, non-volatile, species-specific molecules such as those found in body secretions. These chemicals can work as pheromones, which are released by one horse to produce automatic hormone-like reactions in another.

Warm-Blooded: Lighter, longer-limbed, more slender format. Extremities are longer, manes and fetlocks are less abundant, though this trait is less marked than in the kyang or donkey. The coat provides less insulation and is silkier. The blood vessels can be clearly seen through the skin, which is thinner. The animal is lean, more difficult to fatten, is excitable and less sociable with its fellows. It is capable of sudden, high-powered effort employing anaerobic metabolism. It then mobilizes considerable glycogen reserves in its muscles. Examples: the Dutch Warmblood, Hanoverian, Oldenburg, Trakehner, Holsteiner, American Warmblood, Belgian Warmblood, Irish Sport horse, Gelderland, Mecklenburder, and Austrian Warmblood. Compare Cold-Blooded.

Wild. Living in the wild, and not descended from domesticated animals. Przewalski’s horse now in the steppes of Mongolia is wild. It was never domesticated, and after becoming extinct in the wild, some survivors were bred in captivity and later reintroduced. The mustangs in the American West are feral, not wild.

Weanling. Foal under one year old but no longer nursing.

Winking. Rhythmic contractions of a mare’s vagina, flashing the red color of what’s inside. Mares may spread their back legs slightly, and squat a bit during winking.

Wishful thinking. Closing the gap between belief and desire, expect and hope, by believing what we wish were true. Wishful thinking is not thinking at all. Fishermen like to believe that fish have no feelings, and a hook in the mouth causes them no discomfort. Equestrians like to believe that a bit in a horse’s mouth causes the horse no discomfort “when used correctly.” I know that any time I find myself believing what I wish was true, that I’m likely wrong. I do not think people should make stuff up when relating to another animal.

Wolf teeth — up to 4 rudimentary teeth in front of the first molars in horses.


1 Modern instances of this can be found, by some, in a recent presidential campaign in the U.S. See “Big Lie”; “Joseph Goebbels”.

2 Quotation from Langlois, B. “Inter-breed variation in the horse with regard to cold adaptation: a review.” Livestock Production Science 40.1 (1994): 1-7.

3 Matlin, Margaret W., and David J. Stang. The Pollyanna principle: Selectivity in language, memory, and thought. Schenkman Pub. Co., 1978.; Matlin, Margaret, and David Stang. “Pollyanna principle.” Psychology Today 11, no. 10 (1978): 56.


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