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It doesn't matter what order the suits or numbers are in. Stack the cards neatly in 1 pile, so that all of the black cards are at the top of the deck and all of the red cards are at the bottom. You can also put the red half on top of the black half. Whichever way you choose, make sure you remember which color is on top. Set this up before your audience is there. Otherwise, they'll know how the trick is done! When you hold the cards out, remember which side of the deck is your red cards and which is black. Tell your audience that they can choose any card in the deck. If you fan the cards to the right, then the black cards will be the right half of the deck if they were originally the cards you put on top. This is key to making the trick work. You want to know what color the audience's card is so you can find it later. For example, if the red cards are on the left half of your fanned-out deck, then you know your audience chose a red card if they pull from the left side. If you notice that your audience member is reaching for the middle, subtly shift your hand so they take 1 from the left or right instead. If they pick a card from the center, you might not be able to tell what color it is. Showing you the card defeats the purpose of the whole trick. You can even close your eyes or look away to ensure you don't see it. If they accidentally do reveal the card, start the trick over. If your audience member chose a red card, pull the deck apart in the black section and ask them to place the card there. This ensures you'll be able to locate the card in the deck. Don't put the card back in the deck yourself. Otherwise, your audience might accuse you of rigging the trick. Keep all of the cards face down the entire time. For example, if they picked a red card, their card should now be the only red card in the black half. If they selected a black card, it will be the black card among all the red cards. If you don't see an opposite-colored card in the deck, you've messed up the trick somewhere along the line. Ask your audience if you can try again. You can say something like, "Hmm it looks like you have your own magical powers, and the card has completely disappeared! Try picking another one, but only touch it with 2 fingers so your magic doesn't rub off on it again." Hold the cards so only you can see them while you look for the card. You don't want the audience to see that you've split the deck by color. To finish the trick, hold up the audience's chosen card or lay it down on the table so they can see it. Ask them to confirm that the trick worked, by saying something like, "Is this your card?" You can even add a "ta-da!" for extra flourish. To repeat the trick, reorganize the cards so they're separated by color again.
Sort a deck of cards by color and put the black half on top of the red half. Fan out the cards face down and ask your audience to pick a card. Observe which half of the deck your audience pulls a card from. Ask the audience to look at the card while keeping it hidden from you. Split the deck and have them set the card in the half that's the other color. Look at the cards to find theirs, which will be the 1 opposite-colored card. Reveal the card to your audience.