He held the empty plastic water bottle with one hand, and pulled a drinking glass to the middle of the table between us with the other. He placed the bottle on top of the glass in perfect balance, then rotated the glass. The bottle stayed stable, not moving on its own, only having the same motion as that which he had caused for the glass, as if it and the glass were one object.
He said: “See? Nothing happens at perfect balance.”
He then skewed the position of the bottle a little bit, so that it settles on the glass top at a point closer to its nozzle, one of the extreme ends of the bottle. Now with a very slight twirl of the glass, the bottle on top rotated all on its own, drawing a three-dimensional infinity sign in the space around it, while still being considerably stable in its place. It had more degrees of freedom, allowing it to dance.
We watched it smoothly transpose itself on the glass without needing to cause its motion.
He went: "Wheeeeee!".