Box'ing is a principle that allows us to reveal a spectator's selection using a card box.
You show an empty card box and a deck of cards and hand them both to a spectator. They select a card and bury it back into the deck. Now you say that you are going to find their card using the card box. You then take the box and shake it. They hear nothing. Now you slowly tap the box on the deck and gradually a rattling sound is heard from silence which suggests that something appeared inside. Now they open the box and find a corner of a card there. Now the spectator removes their selected card from the deck and it has a corner missing which matches the piece from the box. You can also do a penetration effect where you rip off a corner from a spectator's card to penetrate the card box.
For your consideration:
2)Everything is examinable
3)Show the box completely empty
4)The spectator holds the box at all times
It is a great effect to do anytime. Check this out!