It's not shape, it's more "texture" and connectivity. The untrained eye can distinguish memory, which is very regular, from other things. The trained eye can

It's not shape, it's more "texture" and connectivity. The untrained eye can distinguish memory, which is very regular, from other things. The trained eye can distinguish some of those other things. You can also partition by texture. Knowing the identify of some things helps you identify what they're connected to. The more that you identify, the more constrained the possibilities are for the remaining things.