The guy who did this made a guide on instructables.com, I can't find it now. It's a real trick, here's the gist of it. To start he has a blue card on the bottom, and the matching red card just above that; he has you pick a 'random' card and does a Hindu shuffle (pulls the cards off the top, while keeping the bottom intact. He then places the top card (the blue one) on top of your card. He spread them and lo-and-behold, a blue card has appeared. Now here'e where the trick get's 'tricky' and the performer's true skill shows through. After gathering up the cards and keeping the blue card on the top (and now the corresponding red card on the bottom), he (very skillfully) performs a double lift. That is, he lifts the top two cards so that you see the front of your card, and the back of the blue card. If you've tried more complex card tricks, you'll know how hard it is to do a double lift as smoothly as this guy does. He then puts the cards back and tosses the blue card (not your card) onto the table nonchalantly. Now he pretends to redo the trick. He does a Hindu shuffle again (remember, the red card corresponding to the blue card is still on the bottom). When you tell him to stop, he simply shows you the bottom card, which he hasn't been changing, so the same card will come up no matter what. He finally gather's the cards, spreads them out, and a blue card is missing. He turns over the existing blue card and Voila, it has magically turned into your second card.