Effect

The performer calls one volunteer to the stage.

He and the audience are shown two decks of cards. 

The performer concentrates on one deck of cards, removing one card from the deck, claiming this card is predicting what card will be chosen from another deck.

He shows the prediction card to the audience, who see the card is black. 

The performer brings out the other deck; the one the volunteer chooses from. The performer shows this deck to the audience only, who see that this deck is an entire deck of cards that match the prediction card! 

The volunteer is asked to say, "stop" while the performer removes one card at a time from the top of the deck and places it on the bottom, showing each card to the audience as he does so. 

The chosen card is slipped into the volunteer's hand, and he names his chosen card. 

To the performer's dismay, the chosen card does not match the black prediction card, or any of the cards in the forcing deck.

 The performer studies the chosen card, baffled. 

However, when he picks up the prediction card, the audience finds that the prediction card has changed, and now is the same as the volunteer's chosen card!