In this trick 16 cards are placed face up on a table, in four rows of four cards. Ask a spectator to pick a card in his mind, and to tell you only the vertical column in which the card is located. Gather up the cards, making sure to pick the fourth vertical column first. (Take the top card in your hand, face up. Pick up the second card and put it onto the first card. The third card goes on these, and then the fourth.) Place those four cards face down in a pile. Next pick up the third vertical column and place it on top of the pile. Repeat this for the second and first columns.
Next deal out the cards in four rows of four, only this time make sure that the first four cards go into the top row, the second four cards go into the second row and so on. You must remember which column (1,2,3 or 4) contained the card. By remembering this you now know which horizontal row contains the chosen card. Ask the spectator to again state which vertical column (1,2,3 or 4) contains his card. The intersection of this column with the original row is the spectator's card. You can pick out the card immediately. In this case the spectator's answers provide us the final row and column of the card.
Most people will see through the magic in this trick in a hurry, though it might remain a mystery to first graders for a long time.