Oh, that's really a cute picture! I know everyone is tired of me talking about Muffin (RIP) but that is what I meant when I said she was such a happy little dog. If you watched her when she was running around the house, that's the way she usually had her mouth -- in what I call the famous yorkie smile.
I believe it is probably something you'll grow used to seeing as your puppy gets older. At least, I hope so. They are generally happy little dogs.
