A person's head is situated on an otherwise empty table. The head talks, moves, is obviously alive. The underside of the table is visible and there's nothing there.
The table is covered with a red cloth which hangs down in front several inches. The floor under the table is covered with straw or some material with no pattern or a completely random pattern. The person to whom the head is attached is seated under the table on a small stool, with legs in the kneeling position if necessary. The key to the illusion is the mirror, which goes from floor to table, from one front leg to the opposite rear leg. It reflects the floor, making the latter seem continuous; the overhanging cloth, to give the impression that it's at the back of the table also; and the free leg of the table, to make it seem as though there are in fact four legs visible.
The spectators can approach quite closely to the table but must be kept from touching it: some mumbo-jumbo about the delicately-positioned arteries of the head being endangered if the table is moved should be sufficient. Care must be taken with the joining of the mirror to the table legs: there must be no visible tatters in the leg sheathing. And of course the mirror must be scrupulously clean. Curtains on either side of the table are used to keep the spectators from getting alongside of the table and so seeing the trick.