The police investigators, Sophie, and Langdon have all been in the same room with Da Vinci’s Mona Lisa without realizing that the painting is central to discovering Saunière’s secret. The Mona Lisa has historically been associated with secrecy; Mona Lisa’s half-smile is famous for its ambiguity, and the sfumato style of painting, which produces a foggy effect, increases the sense of mystery. Many have speculated about the cause of Mona Lisa’s smile. Some, like the young Sophie, have failed to understand the painting’s fascination. Like the meaning of the Mona Lisa’s smile, the secret that Saunière knew seems to be hidden in plain sight.
Brown does not reveal the details of the terrible act Sophie witnessed her grandfather performing. At this point, it is impossible to know whether the act was as horrible as Sophie says, or whether there is some sort of Priory-related explanation for it. Brown has portrayed Sophie as a fairly open-minded person, which suggests that her interpretation of her grandfather’s behavior is probably accurate.
Silas, like Fache, has failed to see that the women around him are not necessarily just unthinking, silent witnesses. Sandrine, like Sophie, has been able to use men’s underestimation and her placement near the scene to exert influence on the action.
Modern communications present an interesting contrast to the ancient signs and symbols that preoccupy the book’s characters. Fache’s use of the cell phone as the way to break the code of Sophie’s betrayal has more in common with modern-day spy movies than with the ancient mysteries that the rest of the novel explores.