A thaumatrope is a Victorian toy based in optical illusion — specifically, the persistence of vision (when visual perception of an image continues even when the image is no longer in sight) — that consists of a two-sided disk on a string that, when twirled swiftly enough, creates the illusion of one combined image, like so (spoilered for the motion sensitive):
The bird-in-cage motif is probably the most well known thaumatrope design, but they also often included riddles or poems; trees-and-leaves, flowers-in-vase, and person-in-house motifs; and, yes, even pornography.
Want to make your own? It’s easy! You just need scissors, glue, a hole-punching device, and a rubber band or string (or even a straw in place of the more traditional string).
Richard Balzer boasted an extensive collection of thaumatropes and other pre-cinema objects, donated to the Academy Museum of Motion Pictures upon his death in 2017. Here are a few fun ones from back in the day (every third slide is a gif, FYI):
So if you get bored, why not try your hand at making a thaumatrope? But they better not all be porn!