Mrs. Smith needed to have her piano tuned so she asked a friend for a recommendation. She then made an appointment with the piano tuner, Mr. Opperknockity. He arrived two days later, tuned the piano satisfactorily, and left.

Shortly after that, Mrs. Smith noticed that the piano was terribly out of tune again. She called the tuner to complain about it and to ask for a return visit to solve the problem.

However, the tuner replied, "I'm sorry ma'am, but Opperknockity only tunes once!"