A deck of cards is fanned, showing both fronts and backs. The spectator is asked to merely think of one card in the deck. The magician introduces a black marker pen and tells the spectator that he is going to turn his back, and mark with an “X” the card that he thinks will be selected by the spectator. This done, the spectator is asked to name the chosen card, and sure enough the magician finds the card in the deck and reveals the mark. Self Working!
