"Go ahead," said the doctor. They made love. "You are making love perfectly," the doctor said. "That will be $10."
They came back six weeks in a row and did the same thing. On the seventh visit the doctor said, "What are you coming here like this for — I told you that you are making love properly!"
"She can't come to my house," said the man, "and I can't go to her house. A motel costs $20. You charge us $10 and we get $8 back from Medicare."