You hand someone a deck of cards that are still in the box. Tell anyone in the audience to think of a card ... just THINK of it ... doesn't matter what it is. Then you open the box, spread the cards out and ONE card is upside down - the card they're thinking of.
Imagine a spectator mentally choosing a card - and yes, they have complete freedom of choice. Next, imagine picking up a standard deck of Bicycle cards and gently thumbing through the pack, to find one card is face-down in an otherwise completely face-up deck. Imagine the reaction when that card is shown to be the spectator's chosen card - the one they merely thought of.
This illusion is surprisingly easy to perform and has been used to astonishing effect on TV by David Blaine and Paul Zenon.
Comes with a special, RED BACKED regulation Bicycle deck of cards (poker size).