Doctor got fooled

 An elderly couple went to the doctor's office. The doctor asked, "What
 can I do for you?"

 The man said, "Will you watch us have sexual intercourse?"
 The doctor looked puzzled but agreed.
 When the couple had finished,  the doctor said, "There is nothing wrong with the way you have
 intercourse." And he charged them $20.
 This happened several weeks in a row. The couple would make an
 appointment, have intercourse, pay the doctor, and leave. Finally the
 doctor asked, "Just exactly what are you trying to find out?"
 The old man said, "We're not trying to find out anything. She is
 married and we can't go to her house. I am married and we can't go to
 my house. Holiday Inn charges $32. The Hilton charges $37. We do it
 here for $20 and I get $18 back from Medicare for a visit to the
 doctor's office."