Horses are herd animals. They prefer to live in large groups and use the group for protection from predators. "There is Safety in Numbers!"
Horses are herbivores (they do not eat meat). This also makes them prey animals - that means they are the "food" for meat eating animals like lions, and tigers, and bears (OH MY!)... wolves also.
Because they are a "prey" animal, their first instinct is to leave or "flee" a situation they find scary. As a result, they are often referred to as "flight" animals. For example, if a horse is grazing in a field and a wolf appears in the same field, the horse will run from the wolf rather than staying and fighting the wolf. Being able to leave a frightening situation is an essential element of the horses' ability to survive.
The horse wants to know who we are and where we are at all times so that he knows we are not a predator. Predators typically attack weak point on the horse that are hard for him to defend - the tendons of the leg, the stomach, the neck, and the head. Be very careful when working with these areas. Be firm when you touch these areas - not ticklish. Make sure the horse knows where you are at all times.
The horse has developed many protective characteristics over time. He has wide-set eyes and sees differently from both eyes (called monocular vision). The wide-set eyes give him the ability to see most of the way around his body.
He also has a very advanced sense of smell and hearing. A horse can listen to sounds both in back of him and in front of him at the same time by focusing each ear in a different direction - similar to radar.
Horses also have powerful bodies and legs. The average weight of an adult horse is 1,000 pounds and 14.5 hands tall (each 'hand' is four inches). He can use his powerful legs to kick and strike a predator to keep from being eaten. Being careful around horses will keep him from thinking we want to eat him.
One final reminder - horses sleep standing up most of the time. They only need about 30-60 minutes of REM (Rapid Eye Movement) sleep each day. During REM sleep, most horses lay down. If a horse is awakened suddenly (maybe when you walk too close to him without letting him know you are coming), he may strike out in fear. Start talking to your horse while you are still a few yards away. Never approach a horse from directly behind without letting him know you are there first. This is one area where he can't see you very well. The other area is directly in front of his nose.