Tricky Turvey Bottles, Metal
Two bottles and two metal covers are used. A spectator uses one set and you use the other.
Both covers are shown empty and then placed over the bottles. They are inverted back and forth, the spectator following your every move.
HOWEVER, when the covers are raised, your bottle is always UPRIGHT.
The spectator's is always UPSIDE DOWN!!
Repeat the process as often as they want!.
As a climax, your bottle turns over in its cover, quicker than they can say the magic word.