A very primitive form of animation, one of the many experiments done by the same guy who did a lot of persistence of vision experiments (and killed one of his retinas by staring at the sun). You have a single strip with a bunch of frames, which you put in a loop inside a drum with slots cut out so that through each slot you see a single frame of the loop. (This is a very common thing to see in a Children's Museum.) When you spin the drum (it's on a free-turning pivot) and look through one slot, each frame in turn passes behind it in such a way that it appears that the strip is staying still but the looped animation is being played on each frame. In effect, you get a very short, looping animation.