Scientists think Leonardo da Vinci’s super-fast eye may have served him to catch the enigmatic magic of Mona Lisa’s smile. Historians have long debated of Leonardo’s “quick eye”, but David S Thaler of Switzerland’s University of Basel has tried to calculate it to show how he gave his drawings and paintings mysterious emotional depth. Thaler’s research unveiled how Leonardo’s eye was so keen that he could spot that the front and back wings of a dragonfly were out of sync, a discovery that took slow-motion photography to prove four centuries later. He concludes that Leonardo accomplished selective soft focus in portraits by painting in overcast or evening light, where the eyes’ pupils enlarge to let in more light but have a narrow plane of intense focus.