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All you need to do for this basic trick is arrange the deck in a standard alternating pattern. Flip the deck over so the audience can see it. If you arranged the deck correctly, the top card is one of the regular playing cards. Fan the cards out with a swipe of your hand to show all of the regular cards in the deck.  The trick cards stay hidden behind the larger cards. You can easily reveal them if you aren’t careful, so don’t move too quickly. You can also fan out the cards while holding them. You may find this easier than spreading them out on the table. Another option is to show all of the trick cards, such as when you “transform” the deck into copies. Riffle the deck so the cards still alternate but the copies are under the regular cards. Fan the deck out as you normally would. Use the “astonishing prediction” trick for an easy way to impress others. First, write down your deck’s trick card on a piece of paper for a spectator to hold onto and open at the end of the trick. Then, dribble through the deck. Because of the way the cards fall, one of the duplicate cards will be on top for you to turn over. After completing the prediction, try turning over the entire deck and spreading it out. If you do this carefully enough, you can pretend the deck is normal by hiding the shorter duplicate cards. Start by dribbling or riffling the cards as usual so the copy cards alternate with the regular cards . Let an audience member select one of the copies. Shuffle the card back into the deck, then begin dealing cards face up on the table until the spectator tells you to stop. Finish the “mind blower” trick by either revealing that the chosen card is in your hand or next in the deck. A variation of this is the "blurt out" trick. Have the spectator put the card back in the deck, then dribble through to show them that all the cards are different. Say something like, “Sometimes people forget what card they chose, so remember that you picked the ten of clubs.” Set a trick card in your pocket ahead of time to remove when you finish the trick. Let a spectator pick out one of the trick cards, then immediately put it back into position in the deck. After riffling, announce that “one card is missing” as you slowly pull out the trick card. Turn the deck over and fan it out to show that there are no copies in the deck.  Make sure you keep the copies hidden behind the regular cards in the deck. If you aren’t careful when fanning out the deck, you may end up revealing the trick. Don’t let the audience inspect the deck. For an alternative version, tape the card to your back and pretend like you can’t find it in the deck. Advanced magicians may be able to plant a duplicate card on an audience member. Doing this involves distracting the audience’s attention, such as by talking and doing tricks, while you put the card in place. Dribble or riffle through the cards before letting the audience member pick one of the copies. Have them put the card back, then shuffle the deck. Ask them how many piles to cut the deck into. Have them select a pile and reveal the top card on it.  When you split the deck correctly, all of the piles will have a duplicate on top. It doesn’t matter how many times they divide the deck or which pile they choose. You can have the audience member tell you where to cut the deck or you can do it yourself. Either way works. Ask an audience member to volunteer, but don’t tell them what you’re about to do. Manipulate the deck as needed to get them to “randomly” pick a duplicate and place it in their pocket. Begin calling out the names of random cards. Instruct the other person to say, “That’s not my card,” even if it is. After a few rounds of this, name the trick card to surprise the audience. Tell the audience that you have been training yourself as a human lie detector and are going to prove your talent. It’s a fun trick that engages the audience but doesn’t require anything beyond basic Svengali techniques.
Spread the deck out so it looks like it has no copies in it. Predict the card someone will pull for a simple starting trick. Find a card shuffled into the deck if you need a quick trick. Put a card in your pocket if you want a more interactive trick. Cut the deck into piles if you wish to let someone find a card. Use the "lie detector" trick to identify a card someone chose.