A card is chosen and signed by a spectator. The magician displays a small envelope whose flap has been trimmed off. He then inserts the chosen card slowly but surely into the envelope. The card doesn't fit all the way in and therefore sticks out a little so it can be seen all the time. The magician then reaches into his pocket and removes a large knife, which he displays dramatically. He suddenly stabs the knife all the way through the envelope, ruining it and the card inside.
The magician shows the stabbed envelope from both sides, pulls the knife out and gives it to the spectator for examination. He then slowly withdraws the card as well, but surprisingly it's unharmed. Everything can be handed out for examination.