They're obviously crazy to us. Our illusions might look obviously crazy to them.

And generally humans don't natively know when they're experiencing an optical illusion. They have to be taught it. And in either case, it's not the human vision system that learns the lesson, it's some other part of the brain that learns to discount the vision system's conclusions.

I bet you could do it with sound, too. Imagine producing what would seem like abstract noise – unrelated to anything in the natural world – but with particular structures and sequences of tones optimised to produce particular emotive responses; pleasure, excitement, calm, energised dancing, romantic dancing...

... wait, don't we already do that?