It is the reason horses can become very attached to a goat, a cat or a chicken. Horses and their relatives, such as the ass or the hybrid mule, will also strongly bond with humans, especially if a lot of time is spent together. Each species has a body language with which they communicate with their own kind. Dogs, for example, threaten by showing their teeth, their only weapon. The submissive dog signals subservience by lowering its body position, folding its forepaws and exposing its throat and abdomen, indicating its vulnerability.
Horses are the only common domestic animal whose primary defense is flight.
When threatened they assume a flight position with head and neck elevated, back rounded, hind quarters gather for a sprint, unless they choose to fight. The horse signals submission by assuming a position of its greatest vulnerability, when it is drinking or grazing. The horse, therefore, acquiesces by lowering its head, working its mouth, chewing and licking its lips, Experienced trainers recognize these signs and consider them to be mile posts in training. Just as chickens peck and dogs snarl and snap, and cattle hook, horses exert their leadership by controlling the movement of their subordinates. Movement is life to the equine.