How do 3D lenticular bookmarks work?

Lenticular bookmarks use a ribbed plastic lens laid over specially interlaced images. As your viewing angle changes, the ridges reveal different slices of the artwork, which the eye reads as motion or depth.

• Flip: the image switches between two or more pictures as you tilt it.
• Animation: a short sequence appears to move, like a tiny film loop.
• 3D depth: layered art gains a sense of dimension without glasses.

The built-in movement is why they are popular for promotional giveaways, children's products, and collectibles, since the effect draws the eye the moment the piece shifts in the light.