Fun Pranks, part one

This prank was described to me by my dear departed father, who had a wickedly dry sense of humor and was crazy about practical jokes.

What you do is, you find someone who has taken apart their car or lawnmower and is putting it back together. You then surreptitiously place an unrelated (but it should _look_ related) part or parts down among the real ones. Now find a shady spot to watch and wait. The fun begins when the guy has all the parts put back together but the ones you put down there, and he doesn't know what to do with them or where they should have gone. If you're lucky he may even take it all apart again and start over.

Daddy was always very careful to describe all his pranks in theoretical terms, being the responsible father, so we were never quite sure which ones actually worked and which ones were just brilliant ideas which hadn't ever been tested. So if you ever happen to try this, please report your results.