Bill, an experienced sky-diver, is getting ready for a jump when he spots another sky-diver wearing dark glasses and holding a guide dog on a very long leash.
Shocked that a blind man is going to jump, Bill strikes up a conversation with him, expressing admiration for his courage. “I’m sorry, I have to ask,” Bill eventually inquires, “how do you know when the ground is getting close?”
“That’s easy,” replies the blind man. “The leash goes slack.”