Okay, I have no clue if this is good or not so I will not be offended if you guys think this is bad.
Imagine this:
A pot of clay is shown freely and spectators can investigate it to make sure it’s normal… clay. A cover is then put on the clay and it is set aside.
Then, one spectator shuffles and deck of cards, which can also be examined.
Another spectator chooses a card, and the magician tells the spectators that the clay can read minds.
He gives it a few moments to think and then takes the cover of the clay off. The name of the spectator’s card is printed on the clay’s surface.

Force the card and make a mechanism inside the cover box that stamps to "chosen" card.