Is There a Smile in the Mona Lisa?

A theory that was put forth by professor margaret livingstone of harvard university. She argues that a a lot of a what fas us about thes paintings, because the smile appears differently depending on where you're standing in position to the painting. If you can to look at out of the corner of yor eyes, it seems like there's pronounced smile. Look at her directly, and it's not there. Another interesting thing is that my mental image of the monalisa is smiling more than the actual image seems to be when i look at it.