I see a lot of laymen and kids who know just one magic trick, and it's usually this one, which I'd categorize under "mathemagic": Deal 21 cards face up in 3 rows of 7. Ask the spectator to think of any of the 21 cards. Turn over the 3 rows into face-down piles. Ask the spectator which pile their card is in and put that pile between the other two. Deal separately into 3 rows again and repeat the process two more times. Then, deal down 10 cards. The spectator's card is the 11th card! Shock and wonder! Anyway, I wanted to look up this trick to see if other magicians have found ways to make this plot more interesting. I have kind of an idea for subverting the expectations to a trick that everyone seems to know (e.g.: at the end, the other 20 cards are all blank!). I've seen Mismag's versions with 5 piles and indicator cards, which is okay, but I'm looking for the origins and what else people have done with it. What do you guys think?