Jumbo 2" Wooden Cubio

A large painted two-inch wooden cube threaded onto a length of cord is shown to move freely back and forth along the cord. But whenever the magician wishes the cord can be made to stop at any point along the cord and remain suspended! Even a spectator can command the cube to stop if the performer allows it to do so. But when everything is handed to the spectators to try and duplicate the feat no one will succeed unless they know the clever secret.