Smile? Well I just don't smile period, but if you mean my equivalent of smiling which looks exactly the same as when I'm serious, sad, angry or whatever else, which actually greatly annoys me because I believe that smiling is a good way to cheer other people but since I can't smile when I'm polite it just looks like I'm doing it because I have to and not because I'm in a good mood which I normally am anyway.
But anyway what made me "smile" today was... eh... I can't remember I'm rather forgetful, but I'm sure something made me "smile" today, I mean I was in such a good mood that I didn't scare the cat that was near my house to go away, and I hate cats and normally can't resist scaring them, instead I said "Hello Mr. Cat", so I'm sure I was happy about something.
EDIT: Since I can't figure out what I was happy about, well I just saw a thing called Ninja Mission Force, and I can say that made me "smile", and now that I know how those ninja's actually are I'm not so nervous that they are following me, though I can't say I feel safe.