Bob, an experienced sky diver, was getting ready for a jump one day
   when he spotted another man outfitted to dive wearing dark glasses,
   carrying a white cane and holding a seeing-eye dog by a leash. Shocked
   that the blind man was also going to jump, Bob struck up a
   conversation, expressing his admiration for the man's courage. Then,
   curious, he asked, "How do you know when the ground is getting close?"
   
   "Easy," replied the blind man. "The leash goes slack."