The magic of the Mona Lisa is the fact that everyone sees something different in her smile. Last fall, BoingBoing reported that researchers at the Institute of Neuroscience in Alicante, Spain, believe this is due to a trick caused by the mind struggling to understand different types of visual information, such as size, clarity, brightness and the location of an object.

Luis Martinez Otero, a neuroscientist at the institute, says Leonardo Da Vinci fully intended to create this type of reaction from Mona Lisa's viewers. "He wrote in one of his notebooks that he was trying to paint dynamic expressions because that's what he saw in the street."