What does it mean when a girl smiles with her teeth showing?

[LinkxPeach]

Early, today at Family Dollar. I was in line, and told her, “she’s forgot to put something in a bag.” Then, she looked at me, and smile with her teeth showing.

[SamA_nold]

Depends on the girl and situation, but generally it's a sign of gratitude or appreciation, similar to a head nod, just without the teeth. Maybe she is embarassed of her smile, doesn't like her teeth, is nervous or uncomfortable around strangers, or just didn't smile with her teeth. Either way, it's nothing to fret over

[Guy13]

She is very... very... very happy to see you.