A card is genuinely freely chosen by a spectator and slipped sight unseen into an envelope that is placed onto the performer's hand. By simply rubbing his fingers across the envelope, the magician claims to be able to divine the name of the selection inside, and after a few moments names a card. The spectator takes the envelope and removes the card to reveal the performer is correct.
This is just one effect made possible by this special, versatile envelope stack idea. Simple to make, this gimmick is based on a tried and tested classic principle.
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