Einstein sits next to a man on a long flight.
Einstein says, “Let’s play a game. I will ask you a question, and if you don’t know the answer, you will pay me only $5; but if I don’t know the answer, I will pay you $500”.
The man agrees and the game proceeds.
Einstein asks the first question, “What is the distance between the Earth and the Moon?”
The man doesn’t say a word. He reaches into his pocket, and pulls out $5.
He then asks Einstein, “What goes up a hill with 3 legs, but comes down on 4?”
Einstein thinks about it ...