When you come home from work and Bentley greets you with what you think is a huge grin with his tongue hanging out, that's not a smile. Bentley is perspiring, which is why he pants with that big open mouth, because dogs have no sweat glands for perspiration. Dogs have no facial muscles to transform their facial expressions according to emotional stimulus, so they can't smile! They either have their mouths closed or open, except when angry or threatening, then they can wrinkle their noses. But go ahead and say your dog smiles at you...I do! Hal
Actually, contrary to the common layman’s belief, dogs do have facial muscles; 12 majors to be exact. Of those there are at least 7 that can give a dog the ability to smile although, a smile may or may not mean the same thing as it does to we humans. What we may deem as a smile, may be a sign of aggression or....not. One of the theories that has been floating around recently is that whilst it is not natural for a dog to show pleasure via the smile, dogs learn facial expressions by closely observing their masters. If the person they are most familiar with smiles a lot, the chances of having a dog who perks up his ears and grins is more likely. At any rate, yup, dogs can really smile.
They show a sad face - they show a happy face Saw a dog that smiled on command They are simply fascinating as most animals are
As with people, I think what we might think of as a smile on a dog is actually a combination of a number of factors, including the eyes, stance, etc. People who spend time with their dogs can probably recognize a smile, and it probably has as much to do with other factors as with mouth positioning.