This is a really good trick. I think it's a lot better than the pen through bill. If you're worried
about people catching you or what's in your hand, reach back into your pocket, ditch, and grab the
rest of your keys so when you take back the key you can put it on the keychain. also if I'm doing it
for a couple of spectators I have them memorize a few of the serial numbers and letters of the bill
so when they get it back they know it's the exact same one instead of signing a bill.