This optical illusion is yet another not-so-subtle reminder that everything we think we see is the result of our brain presenting the world to us in ways that are agent-comprehensible (i.e. the product of a filtering process that autonomously presents to us a version of the world that is (mostly) stripped of noise) and thereby evolutionarily adaptive. It's also likely the result of evolutionary limitations and quirks (there's only so much DNA can do with biological matter).

More.