It's kept art lovers amazed for five centuries, but the secrets of Mona Lisa's famous smile have finally been decoded - by a computer.
The painting, by Leonardo Da Vinci, was analysed at the University of Amsterdam using "emotion recognition" software.
It found that the woman in the picture was 83% happy, 9% disgusted, 6% fearful and 2% angry.
The computer looked at features like the way her lips curved and crinkles around her eyes.
It used a programme which has a database of lots of young women, which it used to create an "average" face.
It uses this average as the standard to compare other faces to.
The painting, which is on public display in the Louvre in Paris, was painted between 1503-1506.
It's thought it's named after the person in the painting, who most people think is a woman from Florence, the wife of a man called Francesco del Giocondo.