 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 (qv), who is an accomplished  juggler. The split sculpture was an invention of  Jim Henson (I) (qv) and Debbie the Roboteer (qv) for Labyrinth.  It looks like rocks until Sarah walks to the right place, then it  looks like a giant carving. Developed over several grueling evenings  over hot noisy robots and Plastina Romana at the Robotorium, Inc on  Mott Street in NYC in the early