After a spectator chooses a card and replaces it in the deck, the magician splits the deck of cards into two piles. One pile of cards is turned face up and the two piles are riffle shuffled together, making a complete deck in which some cards are face up and others are face down, despite international gambling community prohibitions against the use of such a deck. After saying a few magic words, the magician spreads the cards and shows that they are all face up again, except for the selected card, which is face down. Locating the selected card is then done with ease.
Triumph is a self-working card trick that uses a special deck of cards. These cards are precision engineered to have three sides instead of the usual two sides, but they are no thicker than normal playing cards. If the deck is spread with the first side showing, the cards appear to be face down. If it is spread with the second side showing, the cards appear face up. If the deck is rotated 180 degrees to show the third side, the cards appear to be half face up and half face down.
The magician has side one of the deck showing when the spectator picks a card. While the spectator is looking at the card and attempting to memorize it, the magician slyly rotates the deck so that side three is showing. Now, when the spectator's card is inserted into the deck it is the only card with side one up in a side-three-up deck.
The deck is split, one side is turned over, and the halves are shuffled together, but this makes no difference because the deck is still showing side three which is scrambled anyway. After showing the scrambled deck, the magician rotates the deck negative-180 degrees, returning it to side one position. It's turned over and spread showing side two -- except for the selected card, which will now be showing side three (in this case, a card back).
The selected card is removed and the magician is triumphant!