You present two chromium rings to the audience and invite someone to examine them. Reclaim the rings.
Take one in your hand and approach the second. Both rings are inexplicably attracted and clamped together !
Move your arm and the lower ring will start to turn.
The audience is doubtful. No problem ! Give someone the two rings.
The spectator will try to execute the same miracle but he will fail. He will surely retry. Nothing happened.
Reclaim the rings. Retry. Yes, you have the magical fluid !
The audience is astonished and is obliged to concede that those rings are totally normal.