Your mind is not playing tricks on you. These amazing animations were done on transparencies. A pair of images were printed on separate plastic sheets your high school maths teacher used, and one was slowly dragged over the other, resulting in crazy moving pictures, like PacMan eating bullets or a running cat.
You can actually try if for yourself. The guy behind the amazing images -- YouTube user brusspup -- has made them available for download on the video page. And now you've fallen down a rabbit hole for the rest of the day. [BuzzFeed]