The spectators are chosen.  The magician has placed a deck of cards on the table.
 
Spectator LEFT is asked to cut off half the deck and count ten cards face down on to the table.  Spectator RIGHT is given the same instructions.  Spectator LEFT is asked to bury his ten cards face up in the center of his half of the deck.  Again spectator RIGHT gets the same instructions. 
 
Both spectators spread their cards.  Spectator LEFT has only seven cards, Spectator RIGHT now has thirteen.  Somewhere there has been a TRIPLE CROSS!