Method using a bent pin in the eraser. See The Conjurers' Monthly Magazine, Vol. 1 No. 11 July 15, 1907, p. 360, for an interesting article on the history of this trick. It was shown to Houdini in 1893 by an unknown magician. Houdini showed the trick to Roterberg, who gave it to Martinka, Wilmann and British dealers. Houdini writes that the originator is unknown, but “perhaps it has some relationship to the old time trick of causing the soldier to rise and fall at command, which is worked on the same principle.” This trick dates back, it seems, centuries, and was performed in Europe, India and East Asia. Ralph Read credited Leipzig with inventing the improved version, with a removable cap, which Hardin marketed in 1907 without permission (according to Whaley's The Encyclopedic Dictionary of Magic, 1989, p. 580).