"Betting Couple" joke

To celebrate their 50th wedding anniversary, an elderly couple booked the honeymoon suite at a posh hotel.
As the bellboy was taking their luggage to the suite, he thought to himself, "At their age, they're booking the honeymoon suite. What a laugh!"
That night, he decided to spy on them, so he sat in the lobby opposite their suite. All night long, all he heard was giggling and clapping coming from their room. He couldn't believe his ears.
In the morning, he apologized to the husband for having spied on them, but being curious, he asked the husband how he could do what he did at his age.
"Well," the husband replied, "it's like this. First I remove all my clothes and lie face up on the bed. Then my wife removes all her clothes. Then... "
"Then WHAT?" the bellboy asked impatiently.
"Grinning, the elderly husband replied, "Then my wife lifts up my penis with one hand and we make a bet."
"You make a BET?" exclaimed the bellhop. "What bet?!?"
Smirking, the husband explained, "If it falls to the right, I win; and if it falls to the left, she wins."
"But, what if it doesn't fall?" asked the bellhop.
"Then we both win!" replied the husband.