Moral of the story is: even people with the same name can often be split upon issues such as this one!
As I said before, I do believe it is a mouth, but I have a somewhat more educated opinion now. The emoticon -.-, like all emoticons, is meant to express an emotion, and the parts of the face that signify emotion are the eyes and mouth. There's a great quote from The Great Gatsby where Nick Carraway says of Meyer Wolfsheim, the jew who fixed the World Series, that he has a "very expressive nose." The oddity of this quote only proves my point! It's extremely odd to think of a nose as expressing an emotion.
Therefore, it is a mouth. Smileys just don't have noses in them :-/