A couple was lying in bed, ready to go to sleep when the wife suddenly sat up and said, "I'm in the mood for some 69."
The husband, feeling frisky, happily obliged and began to position himself. But just as he was about to get started, the wife stopped him and said, "Actually, let's make it a 68 instead."
Confused, the husband asked, "What's a 68?"
The wife replied, "You do it to me, and I'll owe you one."