The mysterious Mona Lisa smile has something in common with a certain beguiling feature often said to accompany convent girls, or at least I think so.
If you look carefully at the Mona Lisa you notice that just beyond the corners of her mouth, up and out to the side of her face, there is a faint band of darkening. This indicates the faint normal undulation of the face there, but particularly during a smile. The artist has effected this in such a way that the fast processing your mind does of a picture, in grey tones and to a coarse resolution but which registers an emotional message, suggests a certain breadth of smile. Quite a wide, broad smile. But when you start to look closely in fine detail at the width of the mouth, the brain registers a different, lesser, degree of smiling. (BTW, does this face remind you of Meryl Streep?)
This gives a strange dissonance, since the mind tends to alternate between coarse resolution and finer resolution as one gazes at any picture, and the emotional message keeps bobbing up and down. The same effect happens around the edges of the eyes. That faint undulating is a feature Leonardo tended to include in his faces, though not all of them smile. The sour-faced girl with a ferret is one non-smiling example; but I think it’s thought the Mona Lisa was a favourite of his, and I think that more subconsciously perceived broader smile was a style he favoured.
What this has in common with convent-taught girls, is, I think, the subconscious perception of an emotional message which seems to disappear when you try to work out what causes it.
Obviously, youngsters tend to copy what they see around them. Girls educated in a convent will of course experience nuns as a dominant example of behaviour. Whatever may be going on in the students’ conscious minds, they will inevitably tend to take on some of the nun’s overt behaviour, and I suggest that nuns tend not to display cynical, sneering, coarse or angry facial expressions (again, whatever may be going on in their own minds).