Self-working card tricks are mathematical tricks that don't require sleight of hand or "magic," and are easy for anybody of any age to perform. Self-working card tricks can also be fun mathematical exercises that can challenge your viewers to guess how they are done.
Magic ESP Card Trick
Announce the card trick, by telling your viewers that you will ask a participant to choose a random number of cards from the deck, and that you will magically be able to predict the number of cards chosen. Ask for a participant to help you with the trick.
Ask your participant to choose a few cards from the top of the deck, and instruct her not to tell you how many cards she selected.
Tell your participant, "I can tell how many cards you have in your hand just by picking up a few cards for myself." Pick some cards off the top of the deck, but be sure that you choose more cards that he did.
Say, "I'll turn my back and we can both count our cards." Turn your back to your participant and turn back around to face her after you have both counted your cards.
While your back is turned, subtract 3 from your total number of cards. For example, if you have 18 cards, your new total would be 15, and you would tell your participant, "I have the same number of cards as you, plus 3, plus enough cards to bring the total number of cards up to 15."
Ask him how many cards he has and tell her, "I have as many cards as you," and deal that many cards from your deck, counting out loud as you deal. Then say, "Plus three more," and deal three more cards from your pile still counting out loud from where you left off. Keep counting out loud and dealing, saying, "Plus enough to bring the total up to 15," or whatever your total number of cards was.
Deal your remaining cards, continuing to count out loud from where you left off.
Slap-Happy Card Trick
Ask your participant to choose one card from the deck. Ask her to memorize the card and place it facing down on top of the deck.
Deal the two top cards face down on the table, side by side. Deal the next two cards on top of the two cards that are already on the table, and repeat until each pile has six cards.
Deal one additional card on the top of the pile on the left, (which has your participant's card on the bottom.) Place the first pile, (with the additional card,) on top of the second pile.
Pick up that pile and hold it facing down. Deal four piles face down. The first pile will have the additional card. Tell your participant, "This pile has an extra card, but we don't need it," and set the first pile to the side.
You now have three piles remaining. Put the third pile on top of the first pile, and put the second pile on top of the other two, making one pile.
Deal out two piles, face down, just as you did with the four piles. The first pile will have an extra card. Tell your participant, "This pile has an extra card but we don't need it," and set the first pile aside.
You now have a pile of four cards. Ask your participant to hold his hand out with his palm facing up. Place the pile face down on his palm and ask him to hold the cards lightly with her thumb on top of the pile. Alternating with your right and left hand, gently and quickly slap the top three cards off his hand.
Ask her what her card is, and ask her to check the card in her hand. It will be the card she chose.