The smile of Mona Lisa has kept people guessing.Someone says that the smile originated(起源于) from Leonardo da Vinci’s mother，Caterina.Others say the smile is quite simple because women were taught to smile so as to add an air of mystery and elegance(优雅) at that time. 3. It can be found in a number of sculptures(雕塑) from the 15th century. No one knows the truth behind this famous painting except Leonardo da Vinci himself，but people are so fond of it and would enjoy guessing.