Zombie is a stage illusion that most people are familiar with, even though they are often unaware of its name. In its modern incarnation, Zombie is generally presented as the floating of a small, mirrored sphere behind a silk held between the magician's hands. The sphere may jump about beneath the silk, appear over its top edge, or fall to the floor at the embarrassed magician's feet.
When this effect was created by the Mongol warlord magician Tar, it was performed with a severed human head. The head would float about beneath a spread yak skin, eventually peeking out from the skin's top edge and, at the performance's gruesome climax, open its eyes in fear and beg for mercy (which was not forthcoming). Pretty nasty stuff. One can understand why the effect has been toned down somewhat for modern audiences.
Even so, the method of floating the zombie has remained largely unchanged since Tar's day. Both silk and yak skin share the property that when they are rubbed against a suitable surface they can build up a charge of static electricity. This charge helps the lightweight ball or secretly-hollowed-out head cling to its covering, making it appear to float in the air.
The only drawback to this method is that if the magician accidentally touches a ground -- say a metal tray or electric guitar -- the charge dissipates and the effect comes to a tragic halt. It is for this reason that some magicians have stopped using the static electricity method and instead use a thin aluminum zombie ball filled with helium (never hydrogen, since the tragic death of Cigarillo the Smoking Magician). This lighter-than-air ball actually has to be contained by the silk so that it will not float up to the stage ceiling, out of the magician's reach.