Offering to show the spectators something a little different and mysterious, you produce a shiny golden skeleton key. You hold the key for all to see, saying that you will demonstrate something strange.
With just a gentle rub you are able to make the "teeth" of the key move around the cylinder! Then, right in front of the spectator's disbelieving eyes, you move the teeth right down to the bottom of the cylinder.
For a great finish you hand out the key for examination and the teeth are seen to be solidly WELDED in the wrong place - there's no way you could have moved them!