What do horse do when they are frighten?

A horse will generally run away when startled. If unable to run away, it will probably show the whites of its eyes, raise its head, draw its ears back, and try to back away.

If the horse feels particularly trapped and threatened, and becomes panicked, it may stamp, or turn its hindquarters and strike with hind-kicks, but this is usually in an effort to free or distance itself from a threat.