Why is my horse rearing?

i agree with previous answers. Just wanted to comment on the egg thing. I tried it once on a rearing horse. Apparently the horse is supposed to think its hurt itself right? And that it shouldnt rear cos it might get hurt(get is blood down the face nonsense that somebody once told me. You know what when a horse thinks it gotten hurt or harm is befalling it it does not stop and go oooh shouldnt do that again it goes oooo my gosh ooo my gosh what the!!!! Freaking out a lot more. Then you end up on the floor like me. Sure he didnt rear me off but he sure as hell bucked. Dunno maybe it was just my horse?