Smile and you will be smiled upon

Just a small observation.
Say you walk around a crowded area, let's pick a train station during the morning commute, did you notice that when you have eye-contact with someone and you pull up the corners of your mouth to a "smile" position, that in most cases the other person is smiling back at you? It brightens my day every time I do it. It's so nice to be smiled to. :-) And I can't help but think that I've, in a very small way, brightened up the day of that other person.

Zaaf