There's a lot of interest in visual illusions at the moment thanks to an excellent article over at Seed, This Picture Is Not Moving.
A while back I wrote about the Hollow Face Illusion in which a hollow (concave) mask of a face appears to be a solid (convex) face and I posted a seriously freaky video featuring Charlie Chaplin. But reader "Jake" just pointed out an even better example of the same illusion, the Paper Dragon.
See the video above. If you like what you see, you can make your own paper dragon by printing out this .pdf here. It only takes 10 minutes, scissors and a bit of sticky tape. I highly recommend it, the effect is astonishing - it really looks as though the dragon's head is moving. You may need to close one eye to get the full experience. (The dragon was designed by ThinkFun).
The dragon, like the Charlie Chaplin mask, is an example of the "depth inversion" effect. Our visual system assumes that objects are convex, rather than concave, especially when those objects are familiar things like faces.
In my opinion the most interesting thing about the phenomena, and indeed with all illusions, is that concious belief cannot override the effect. I know that the dragon's head is concave, I folded it up and stuck it together myself. Yet I still see it as convex. This is strong evidence for the modularity of mind. But that's another story.