Watch | The two faces of Mona Lisa

Is Mona Lisa two-faced?

According to an art detective in Italy, Leonardo da Vinci used two models - one woman and one man - to create the face of his world famous Mona Lisa. Some art historians say that while being painted Mona Lisa looked too sad and efforts to cheer her up failed.

So Leonardo used the smile of a second model known as Salai.

Although painted in the early 1500s, theories about the secret behind Mona Lisa's smile have been debated for centuries.