A man was wheeling himself frantically down the hall of the hospital in his wheelchair just before his operation. 

A nurse stopped him and asked, "What's the matter?" 

He said, "I heard the nurse say, 'It's a very simple operation, so don't worry. I'm sure it will be all right.'" 

"She was just trying to comfort you. What's so frightening about that?" 

"She wasn't talking to me. She was talking to the doctor!"