Since alot of people are saying that they don't get it or didn't see anything, I'll tell you what you should see.
You go cross-eyes and the images kind of duplicate and those duplicates seem to come together in to one, forming the 3 images. Then you focus one the middle one, and it becomes slightly smaller than the other 2, but also seems to pop out, or seem to be 3D. It's very nice if you manage to do it right.