This piece was made to demonstrate the "wagon wheel" effect, also known as "temporal aliasing". This effect occurs when a cyclic motion happens at a rate similar to the frame rate of our vision or a recording device. You've probably seen it happen with hubcaps (or wagon wheels, if you're a cowpoke): the wheels sometimes appear to be turning backward when the vehicle is moving forward.

Start with your mouse at the zero position, and move it slowly left or right. The further you move the move, the faster the film loop will move in that direction. The film only moves horizontally, and is only still when your mouse is at zero. If the film appears to be still or moving the wrong way, you're seeing the wagon wheel effect. [requires Flash 5]