The rope tie ring. Wear this ring to one of the spectators on hand. Ask him to change the position of the rope, in other words, to make the ring "eight", not removing his hand. "Volunteer"will likely not be able to do it. Then it make you his own hands, without removing the ring.
But to make it simple. The upper part of the ring down, wrap it around the bottom, lift up and with the same hand wear portion on one of your hands. The first loop with hands clear. The result will be "eight":