My father once told me about watching a garage mechanic deal with a dent in a bumper. Dad had taken his car to Bunnell's Garage (in Nottingham, New Hampshire) because the car had begun to have a little shimmy.
Bunnell: "It sounds like you need your wheels aligned."
Dad: "Well, I had them aligned several months ago at (here he named a national chain)."
Bunnell: "Ha! All that means is that when you stop for a red light your front wheels won't fall off."
Bunnell was holding a rubber mallet and told Dad, "I'll be with you in just a minute."
He walked over to a car with a dent in the rear bumper. This was in the early 1960's when bumpers were made of sterner stuff.
The dent was about a third of the way in from one end, and Dad watched as Bunnell bent down and looked at the dent, put his hand behind the bumper at the dent's location and felt around, walked to one end of the bumper, walked to the other end of the bumper, and then gave that end a thump with the mallet. The dent popped right out. Bunnell looked up at my father and said, "That is the principle of lever and fid."
He and Dad had known each other for years, and Dad told him, "It happens that I know what a fid is, you old fraud."