I remember people trying to do it as a kid by putting their noses in the books, and it confused the hell out of me. But then when I’d explain how to do it, they acted like I was muttering moon speak.

But what I do is just make repeating shapes overlap. Like, have you ever made your fingers overlap (by crossing your eyes)? Or played with the double images of things near your face while looking at something in the background?

You just do that so that neighbouring copies of image elements overlap.