Things I've been known to leave in Out-Of-Office auto-replies in order to see if people pay attention to them:
"What is the airspeed velocity of an unladen swallow?" - You mean an African or European swallow? Anyway, someone else went to the trouble of figuring it out: http://www.style.org/unladenswallow/
"What happens if I drop a Gummi Bear(TM) in a glass of water?". Well, after a while it looks like this: http://www.chrisnull.com/gummi.gif