The Darwin fish symbol and the levitating water illusion both have Al Seckel in common.
In this TED talk, Seckel tells us our brains are mis-wired: "Our expectations are violated in some sort of pleasing way."
His book Masters of Deception: Escher, Dali & the Artists of Optical Illusion>>
Some of Al Seckel’s books>>
Al Seckel at Wikipedia>>