Optical illusions are proof that while the human eye is a wondrous feat of natural design, a biological marvel and rather damn useful for getting around - they're not beyond being tricked.
Artists, psychologists and scientists have reveled in devising fiendish pictures that leave us rubbing out retinas in disbelief for centuries - whether it's fusing two pictures into one, making two dimensions pop into three or causing colours and shapes to dance like they're alive.
But all of them prove that the world around us isn't always as straight forward as we might think. Enjoy.
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