Sorry i should have explained more. If you put it on the bottom of the deck, you can show all the cards to be faced down. and if you can secretly turn it over with some misdirection or the cover of your hand, it looks like the deck is still face down. So, for instance, you could tell them to put his or her selected card in the deck face down, when in actuality they are putting it in face up in with the rest of the cards, which you can just turn back over and now there card is the only face up card in teh deck.. That is just one little use.