The next morning, he asks the old man how he can do it all night at his age.

The husband replies, "First, I remove my clothes. Then, I lie down on the bed face up. Then, my wife removes her clothes and lifts up my penis with one hand, and we make a bet. If it falls to left when she lets go, I win; if it falls to right, she wins."

The bell boy asks, "Well, what if it doesn't fall?"

"Then we both win," says the old man.