Card Trick Demonstration
Card Trick Demonstration
This trick demonstrates how a deck of cards can act as a computer, tracking your input and finding your selected card through elimination.
How the Trick Works
Make up a small deck of twelve cards as follows: Use the ace through six of spades and the ace through six of clubs. Arrange these as if they were a new deck: The ace of spades on top followed by the two of spades, and so on, ending with the six of spades. Then the clubs, in reverse order—the six of clubs, followed by the five of clubs, and so on, with the ace of clubs on the bottom.
The packet is going to act as a computer. It needs some input from you. Think of a small number, say, two, three, or four; deal the packet of twelve cards into that number of piles, face-down on the table, from right to left. Reassemble the piles into a single packet by putting one on the next (left to right, or right to left). Repeat once more—think of a new small number, deal that many piles, and reassemble.
The next step of mixing involves a reverse perfect shuffle. Hold the packet face-down as if you were about to deal them in a card game. Spread through the packet, pushing out alternate cards. When you are through, remove the forward cards as a group and place them on top.
The packet of cards is tracking your input. When you are done shuffling, let the computer know by performing a Monge shuffle. To do this, hold the packet in dealing position. Deal the cards from one hand to the other as follows: Push the top card off and take it in the opposite hand. Push the next card off on top of the first card. Push the next card off and put it underneath the first two. The next card is placed on top, the next underneath, and so on until you are done.
To select a card, hold the cards face-down in dealing position. Start moving cards one at a time from the top of the packet to the bottom. Stop whenever you want. The current top card is your choice. Deal it, face-down, off to one side.
The computer will now find out which card you picked by a process of elimination. This final elimination phase uses the down-and-under shuffle. Hold the eleven-card packet face-down in dealing position. Deal the top card down onto the table. Put the next card under the packet (from top to bottom). Deal the next card onto the table, put the next under the packet and so on. This eliminates cards one at a time until one card is left in your hand.
You have selected a card freely from a mixed deck and the cards have determined a card from those remaining. The two cards should be a match in value—like the two of spades and the two of clubs.