A woman bit my thumb?

Long story short, I was with a lady friend last night after she got home from the bar so we could watch a movie together. She was quite intoxicated, so I think that had most to do with it. Anyway, tonight, she was much more cuddly than usual and snuggled up/layed against me and held both my hands with her own and squeezed and massaged them both continuously. I wasn't paying much attention until she moved her head lower and lifted my hand up to her face and I could feel her lips mouthing my thumb and then she stuck it in her mouth and bit it. Not hard, but hard enough to get my attention. I remained silent and just let things take their course. She then kissed my thumb and let my hand back down again.

What was that all about? Please be serious, I don't want to see answers like "She wants the D" and all this other bullcrap because that is just immature. Thank you!