The  Classic Effect

Two Chinese coins are displayed, one is red, and the other is black.

The coins are displayed in the left hand, then the hand is closed into a fist. The magician reaches inside the fist and removes the black Chinese coin, and places it in his pocket. The spectator is asked which coin remains. They, of course, reply, "Red." The magician opens his hand to reveal both coins – red and black!

This is repeated with the magician removing the red Chinese coin. Once again, the hand is opened, revealing both coins remain. Again, the black coin is removed, then magically, it returns.

Finally, the red coin is removed once again. When the magician opens his hands, both coins have vanished!