This is a routine that i came up with its really interesting yet very simple to perform.
you borrow the deck of cards from a spectator and ask them to shuffle their cards. now you take the deck and place it back into the box and hand them over their deck. Now you introduce your deck ask them to remember a card as you riffle through the pack. they got a card. now you ask your spectator to think of that card is turning upside down in the deck that they are holding. They do so. Now you ask them to open the box and check the cards the thought card is upside down in the entire deck. now you show your deck that card is also upside down in your deck.
this trick consist only on one sleight The Force. Use any force you like but riffle force the same force that is used on tv by the magicians when they perform magic for you they riffle the cards and ask you to when you see a card just remember it.
when you ask to borrow the deck from spectator you ask the to shuffle the cards they do it. now you take the deck from them and introduce your deck to them and ask them to shuffler your deck as well. as they are doing this simply turnover one card in the deck you want to force.
when they shuffle your deck give their deck back to them with turn over card inside the deck. ask them to put the cards in the box. and hold on to it.
now from your deck your riffle force the selected card. ask your spectator to imagine that their card is turning over in their deck.
they do so. now you ask them to open the box and look for their card. as they are doing you also turn the forced card in your deck. when they will see that their card is turned over in their hands they will flip now to hit hard you show that the card in your deck is also turn over.