My mom would always have to explain to people that I wasn't sad, I just enjoyed myself more by being observant. Even as a baby I showed very little facial concern.
I had to look for myself through my baby pictures (5 and under) to see if I was actually smiling in some of them. Only about a third, and even those were little sardonic half smiles, like someone just told me a corny pun. I never noticed before, but in most my baby pictures I'm playing alone. Holding a balloon slack faced, checking under a rock, sadly staring at a jack-the-box, holding a cat or dog looking the other way, huddled up in a clothes hamper. The closest I came to finding a picture of me playing with other kids was one where I'm about 4, I'm with my sister and nephew who are playing on a slide, and I'm just standing there examining some kind of wooden tinker toy in my hands.