Mona Lisa.

Science Back in 2009, New Scientist published research into Mona Lisa's smile and why it seems so, myterio ... enigmatic. Why she seems to happy one minutes, but serious the next. As you might have expected, it's all in the brain:

"Different cells in the retina transmit different categories of information or "channels" to the brain. These channels encode data about an object's size, clarity, brightness and location in the visual field.

"Sometimes one channel wins over the other, and you see the smile, sometimes others take over and you don't see the smile," says Luis Martinez Otero, a neuroscientist at Institute of Neuroscience in Alicante, Spain, who conducted the study along with Diego Alonso Pablos."

When I visited I could barely see her thanks to the picture being shoulder deep in photographic tourists.