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For a basic flip image that changes as you move your head, you need to arrange the lenticles so both eyes always see the same image; as you move your head, both eyes then switch simultaneously to the other image. Adding more images, it’s possible to create a basic illusion of movement (a bit like a flip book) and a zooming effect, so the image appears to get closer or further away as you move the flip lenticular poster back and forth. With a slightly different arrangement of lenticles, arranged vertically, we can send one image to one eye and the alternate interleaved image to the other, giving the illusion of a three-dimensional picture.

Lenticular images are the neato transforming pictures that often came on trading cards in the 1980s and 90s. They were handy for freaking out young children or filing your nails. Turn them one way and they show one picture. Turn them another and they show another. How? A trick of the light. And plastics.