The man said, "Will you watch us have sexual intercourse?" The doctor looked puzzled, but agreed. The doctor examined them and then directed them to disrobe and go at it.
When the couple finished, the doctor reexamined them and, upon completion, advised the couple, "There's nothing wrong with the way you have intercourse." He then charged them $32.
This happened several weeks in a row. The couple would make an appointment, have intercourse with no apparent problems other than the lack of vigor which is to be expected in 67 year olds, get dressed, pay the doctor, and then leave.
Finally after almost two months of this routine, the doctor asked, "Just exactly what are you trying to find out?"
The old man said, "Oh, we're not trying to find out anything. She's married and we can't go to her house. I'm married, so we can't go to my house. The Holiday Inn charges $60. The Hilton charges $78. We do it here for $32 and I get $28 back from Medicare."