According to Scientists, in dogs smiling” is a sign of nervousness and submission. They believe that most animals show emotions through facial expressions, just like humans. Facial expressions are the way our brains move the muscles in our faces to express the way we feel. We raise our eyebrows in surprise, we lower our eyelids in shyness, and we smile with happiness.
That last facial expression is the one we most like to experience ourselves as well as to see in others. Happy dogs have a general looseness to their bodies, and that applies to the mouth area, too. More telling is your dog’s tongue. A loose-hanging tongue combined with a mouth slightly ajar generally points to a good moods in a doggy. Although dogs don’t actually smile like humans, they sometimes happen to make expressions that look like smiles.