Hey folks--back in the 70s (probably before and since) there was a trippy style of producing small bits of pop art that allowed you to see two different images with a slight rotation of the piece. For instance, one view would be a tadpole, and with a tilt you would see it turn into a frog. A ribbed layer of clear plastic provided the optic effect. Holograms weren't available yet, and I always thought these things were so cool as a kid. Often they were the size of a baseball card or smaller, though I do have one that's 10" x 12". Sometimes they'd be freebies in a box of cereal or ice cream sandwiches.

The question: does anyone know what these things are called? I have a piece of art that I've created and would like to have manufactured into prints of this type. It sure would help to know what to Google!