You need some set-up for his trick. At the start, the deck of cards is secretly separated into two groups - one set of cards with values that are prime numbers and one set of non-prime values. By doing this, you will easily be able to tell exactly what cards were swapped but your spectators won’t notice. So start by dividing up the deck with all the prime numbers in one stack (2, 3, , 7, J, K) and the non-prime in the other (A, 4, , 8, 9, 10, Q). Keep the suits of the cards in a nice.
