I'm catching up, I actually made this quite a while ago. It's a very simple propeller mounted on a pin.
It spins in the warm air rising from my monitor.
I bent part of the mysterious pin thing (bottom) and taped it to a piece of paper as a base (middle). The base has a paper finger which pokes
into the grill on top of the monitor and stops it sliding. The propeller is a simple rectangle with two slits cut in it and flaps folded down (top).
Here's an animation!
(This was inspired by Dan's over-the-heater twisty-turny thing.)
