The only known way to kill a purple horse is to cut of it's tail and then make it into won tons that go in a soup that you then feed to the horse. No tests with guns or knives have been conducted as of yet because the soup one was more practical.
person b) noo! that's a purple horse! it'll eat your brains!
person b) timmy! noooo
person a) my brains are being eaten!
horse) mmm BRAIIINZZ!
person b)Ah well, I never really liked timmy all that much in the first place.
person c) yeah. neither did I. Thanks purple horse.