Two small brass boxes, each adorned with a distinct jewel are displayed and passed for examination. While your back is turned, ask a spectator to place some small object into one of the boxes, then replace the lid on the box. Before you turn around, ask him to mix the boxes. Turn back to face the audience. Without asking any questions or touching the boxes, you are able to immediately locate the hidden object. This feat of mental power is "performed with the aid of a natural crystal which you hold above each box, interpreting the vibrations." The effect can be repeated with another object. This time the spectator actually hides the boxes from your view. Yet, you are able to once again divine which box holds the hidden object.