While new optical illusions go viral all the time, here are some of the most famous illusions that have kept us scratching our heads for years.

Most people use the terms “optical illusion” and “visual illusion” interchangeably, much like “fluid” and “liquid” or “sofa” and “couch” are synonyms. At first glance, this might be seemingly pedantic ...

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Everyone loves an optical illusion — even if they leave us completely stumped — and they're all around us in the natural world. From an underwater waterfall in the Indian Ocean to a surrealist scene ...