It has been found that Mona Lisa's smile becomes more pronounced when the observer looks into her eyes and disappears when he looks directly at her mouth. This difference is experienced because the human eye perceives the world in two different ways. When we look directly at an object, the light falls on the central part of the retina, allowing us to see relatively bright objects. On the other hand, when we look at something from the angle of the eye, the light falls on the outer part of the retina, which allows us to see the half-shadows better.
