Okay, here’s one for you in honour of April Fool’s Day.
Take a penny out of your pocket, lick it and stick it to your forehead. “Water has amazing adhesive properties,” you say.
Take the penny off, moisten it again, and stick it on your friend’s forehead. “See if you can get it to fall off without touching it.”
So your friend gets going with the eyebrows and cheek muscles and so on.
What your friend doesn’t know: when you took your hand away from his or her forehead, you took the penny away with it.
Feeling the moist spot and thinking the penny is still there, your friend keeps on making the most ridiculous faces.
“Hey guys, come over here and watch this,” you say. Offer no explanation.