Can you figure out how this is done before the secret is revealed? There's no threads, magnets, blowing or electronics involved. Please don't leave any clues in the comments and share it with your friends - they won't be able to figure it out either. Enjoy!
Wow. I was just re-reading my Vernon Touch book and Vernon describe this exact effect. He said Welsh Miller would do this with a card climbing up the wall at Max Holdens shop and nobody could ever figure it out. (Genii, March 1970)
The reason this came about was that I saw a really lazy fly on the floor at the supermarket. I went to step on him but he didn't even fly away... just continued wandering. So I dropped a price tag on him and he just walked around and it moved.
I whipped out the iPhone and the rest was "magic"! ;)