You ask your spectator to deal 4 cards into 4 piles and shuffle every pile separately. Then ask him to eliminate any 3 piles.
Now you have 3 options:
1. Predict 13 cards: The last pile has a prediction on a paper with 13 cards written on it.
2. Memorize the chosen pile: Now you are ready to memorize the last 13 cards in 10 seconds. It is so easy.
3. Focus: you will focus on the rest of the deck and you will know the cards in remaining pile.
In this download, you will get 6 tutorial videos and PDF.