Parabox by Jerry Andrus is one of his more famous optical illusions. Hold it at arm's length and close one eye. In a second or two, the concave image of the crate will become convex, or dimensional. Also,

A spectator selects a card from an ordinary deck. The performer displays a small solid crystal cube, which he explains will condense and focus thought rays, just like a lens focuses light rays. The cube is held between finger and thumb, right under the