An old couple goes to the doctor. The man says, "We want to know if we're makin' love properly. Will you watch us?"
The doctor says, "Go ahead." So they go to it.
The doctor says, "Looks good to me... That'll be forty dollars."
They go back six weeks in a row and do the same thing each time.
On the seventh week the doctor says, "Why do you keep coming back? I told you, you're making love perfectly."
The old guy says, "Well, she can't come to my house, and I can't go to her's...a motel is fifty bucks...you only charge us forty and we get back thirty-five back from Medicare."