There are a LOT of different kinds of smiles. Only a few of them are happy / indicate happiness. Scientifically, even. As in microexpressions transcend cultural barriers. Smiling with a 1/5th of 1 second twitch of your upper lip? Actually indicates disgust and revulsion. But a twitch on the corner of the mouth? Nervousness. Smiling while touching your eyebrow? Shame. Smiles that bare teeth? Are as likely to indicate anger or fear (adrenaline response), as happiness. Not a 50/50 thing, or even a 33/33/33 thing... as there are social smiles that indicate no emotion whatsoever... And social smiles that are defense mechanisms... And defense mechanisms that show up as smiles (2 different things, truly, one is putting on a front for the world, one is more strength to self). Helluva lot of different reasons people smile.
If you don't want to look up the science on it? Think of movies. How many times have you seen sad smiles? Wry smiles? Angry smiles? Hungry smiles? Nervous smiles? Shy smiles? Embarassed smiles? Cocky smiles? Defensive smiles? Busted! Smiles? Joyful smiles? Relieved smiles? Exhausted smiles? Etc.? How do we know what those smiles are? Because actors are deliberately creating the rest of the expression. Both the macro-expressions and micro-expressions. The really subtle nuances create the difference between world class actors and B-Movie "that's wrooooong" expressions. Again, a whole lotta different kinds of smiles.
