I simply ask the spectator to choose 1 random card then put it in the middle of the deck .the deck will be mixed up and divided into 2 parts and both of them will be shuffled one more time After that i ask the spectator to think what pack have his card in it. For example in the performance, the spectator chose the right pack, then i asked the color of their card , they said " red " and every single card from the chosen pack were red but it did not include the spectator's card. In the end , i showed them that the other pack was full of black cards with an exception of one red card which was the selected one