Ask the spectator to replace his part of the deck on top of your pile (still behind your back).
Bring the deck out and run through the cards. Look for the card that you remembered. The card just after this card is the one that your spectator selected. You can now identify the spectator’s card.
Better Magic
When you’re glancing at the bottom card, casually show the deck to the other spectators and mention how there are different cards and that they have been thoroughly mixed. While this makes it look as if you're trying to be fair, it's a ruse that allows you to perform the necessary work to look at and remember the bottom card.
Don't just run through the cards and find and name the spectator's card, offer some explanation or story. For example, tell the spectator that you are looking for his finger print that remains on the card and tells you which one it is.
Or you can pretend to weigh the cards an dtell the spectator that his fingerprint makes his card a bit heavier than the others. Use your creativity here. Remember that it's your creativity and personality that makes the magic. Otherwise, a trick such as this is simply a puzzle.
