Some say that the eyes are "the window to the soul" then what are SMILING FACES?
Perhaps as we look around at who is smiling and who is not we can derive simply that those who are smiling are happy. I think there is a difference between contentment and happy. Feeling happy can be an immediate expression to a thought or reaction to a stimuli that gives that unexpected smile in the face. Contentment can be expressed without a smile. Sometimes a stoic look can mean that the thoughts are pleasing, but not to pleasing that it requires the muscles of the face to erupt into a smile.
If children are happy they have a hard time not smiling unless they have barriers to a smile. Such as in Autism where the connection between what should or could be shown outwardly does not occur in context (most often). Are they smiling inside?
In a social context what can be taught? Is smiling a learned activity?