Lubor Fiedler invented the Gozinta Box. In his trick, the magician shows a box, opens it and takes out the box inside. To the amazement of the audience, the magician opens up what was the inner box, and promptly places inside it the box which started out on the outside. The trick can be repeated to return the boxes to their original positions. This particular Ali Bongo item is a variation. In addition to the boxes changing places, the magician discovers a 50lb weight (or 20kg for continental audiences) and a cannon ball inside.