A spectator chooses a card and loses it in a shuffled deck. The magician spreads the cards out on a table, is blindfolded, and stabs through one of the spread cards with a knife, pinning it to the table. The wounded card is removed and shown to be the spectator's selection. The damaged table is returned to the antiques dealer from which it was borrowed.
This effect, simple as it is, makes use of three subtleties.
First, there is what magicians call a "peek." This is a method by which, after a card is chosen, a magician quickly "peeks" at the faces of the remaining cards. Whatever cards is not there is, by deductive reasoning, the selected card. Q.E.D.
Second, there is a trick blindfold. A favorite is Richard Osterlind's steel blindfold -- made of steel on the outside but clear glass on the inside so that a magician wearing it looks completely blinded but actually can see as easily as if peering through a car windshield.
Third and finally, there is the location of the card in the scrambled deck. This is done by means of a deck of cards that has been put in the oven (long enough to give the cards a bit of curl) and a knife that is very, very shiny. When the cards are spread on the table face down, their edges curl up just enough that the magician can see the reflections of the faces in the side of the knife. Once the correct card is located, it's stabbed, and a miracle has been made!
Note: Many orphanages and other charities will happily accept donations of decks with one stabbed card.