The various things that Jareth does with the crystal balls (rolling them around his arms and in his hands and so forth) are not camera tricks or any other kind of special effect. They are actually done by choreographer Michael Moschen, who is an accomplished juggler. Moschen was actually crouched behind Bowie with his arm(s) replacing Bowie's. Unlike a typical Muppet performance, however, he had no video screen to view his performance. In other words, his manipulations were performed completely blind.