A mechanic was removing the cylinder heads from the motor of a car when he spotted the famous heart surgeon in his shop, who was standing off to the side, waiting for the service manager to come to take a look at his car.
The mechanic shouted across the garage,"Hello Doctor!! Please come over here for a minute."
The famous surgeon, a bit surprised, walked over to the mechanic.
The doctor leaned over and whispered to the mechanic and the mechanic was floored.
Can you guess what was whispered by the doctor?
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He said: "Try to do it when the engine is running".