A jockey is about to enter a race on a new horse. The horse's trainer meets him before the race and says, "All you have to remember with this horse is that every time you approach a jump, you have to shout, 'ALLEY OOP!' really loudly in the horse's ear. Providing you do that, you'll be fine."
The jockey thinks the trainer is mad but promises to shout the command. The race begins and they approach the first hurdle. The jockey ignores the trainer's ridiculous advice and the horse crashes straight through the center of the jump.
They carry on and approach the second hurdle. The jockey, somewhat embarrassed, whispers "Alley Oop" into the horse's ear. The same thing happens - the horse crashes straight through the center of the jump.
At the third hurdle, the jockey thinks, "It's no good, I'll have to do it," and screams at the top of his lungs, "ALLEY OOP!” into the horse’s ear. Sure enough, the horse sails over the jump with no problems. This continues for the rest of the race, but due to the earlier problems the horse only finishes third.
The trainer is fuming and asks the jockey what went wrong. The jockey replies, "Nothing is wrong with me - it's this bloody horse. What is he - deaf or something?"
The trainer replies, "Deaf? Deaf?! He's not deaf. He's blind!"