EVERYTHING until it finds out the scary thing is not going to kill it. Remember, the horse is in the same animal category as the elk, deer, rabbit, squirrel, and chicken. They are all prey animals.
What horses fear is just about everything it isn’t familiar with. Any change in their surroundings triggers the flight instinct because of the fear of getting hurt.
Horses shy when they perceive something that they remember as being threatening or when they perceive something that their memory tells them it doesn’t belong there.
So, what do some trainers teach the rider to do when the horse shies and “stupidly” attempts to flee something it perceives as dangerous? They usually ask the rider to make the horse turn and face the scary thing using crops and spurs (oftentimes people use spurs incorrectly. They are to be used for refined communication, not to make a horse do something, actually the primary use of spurs is for lateral movement) the horse is telling us it’s afraid it will get hurt, so we hurt it by using force. This confirms the fear and is why so many horses shy. Does this make sense, ‘course not?
When a horse shows fear, all we need to do is use the correct methods of desensitization to dispel the fear and then use positive reinforcement to make the frightening object a desirable object. The horse’s behavior can be shaped or modified, if correct methods are used.
When we persist in using improper techniques/methods, even if they are more natural to us because of our instincts, predator behavior, then getting the horse to do what we want may take many hours, days, weeks, or months or never.
Frequently we will fail, usually satisfying ourselves that the horse was stupid, obstinate or a poor learner.
Learn the correct ways of teaching a horse taking care not to give it a bad experience. Teaching horses should be a thing of beauty, if it isn’t, you’re doing it incorrectly.