A woman surgeon was disturbed about the high cost of her car repair.

"This is ridiculous!" she said, "charging me five hundred dollars to grind the valves and put in new piston rings."

"Not really, just think about it.  You are a surgeon and should know that an automobile engine is just as complicated as a human body.  The mechanic who serviced your car is just as skilled as you are."

"Is that so?  Well, let me see him grind valves while the engine is running."