Arthur is 90 years old. He's played golf every day since his retirement 25 years ago. One day he arrives home looking downcast. "That's it," he tells his wife. "I'm giving up golf. My eyesight has gotten so bad. Once I've hit the ball, I can't see where it went."
His wife sympathizes. As they sit down, she has a suggestion: "Why don't you take my brother with you, and give it one more try." "That's no good," sighs Arthur. "Your brother is a hundred and three. He can't help." "He may be a hundred and three," says the wife, "but his eyesight is perfect."
So the next day, Arthur heads off to the golf course with his brother-in-law. He tees up, takes an almighty swing, and squints down the fairway. He turns to the brother-in-law. "Did you see the ball?"
"Of course I did!" says the brother-in-law. "I have perfect eyesight."
"Where did it go?" asks Arthur.