Did you ever wonder why a small dog, like a Pomeranian, looks like it's smiling when it opens its mouth. You know dogs, particularly dogs with very thick coats, breath across their wet tongues to cool off, with their mouths open. I thinks it's so you won't kill them.
They're basically annoying dogs, yapping, nervous, busy. Sometimes sweet, sometimes mean. The open mouth makes them look like they're smiling. They're bright eyed and perky, so they look intelligent and attentive. The smile makes them seem pleasant or happy.
I guess it's a matter of the dog's personality fitting the human's.
