You fairly display a deck of cards - they appear to be in a completely random order - before giving your spectator two pieces of information: 1. One of the cards in the deck is "different from all the rest". 2. The deck is in a completely random order but for three cards which you have specifically positioned for an experiment; a test of your participants free will! You begin to deal through the deck, face up on the table, asking a spectator to say "stop" whenever they like. Whichever card they stop on (no force) is used to arrive at a second card and that card is used to arrive at a third. The entire procedure so far has been completely beyond reproach. Here's where it gets weird...
You ask the spectator to turn over one of the Jokers (both Jokers have been on full view throughout.) It correctly predicts the suit and value of the third card! You total the value of all three cards. The spectator turns over the other Joker - is accurately predicts the total! Finally, reminding your spectator of the card that is "different from all the rest", the card they first stopped you on is returned over to reveal the words "STOP HERE" in big black bold letters!
All you need is a regular pack of cards and five minutes to prep it!