Smile
 

My neighbor says her dog can smile. I'm sure the dog can make a face that looks like a smile, but dogs can smile and emotional smile.

Considering that when dogs bare their teeth, they're giving a warning, not sure I want a smiling dog. That being said, there's no question that a dog with an open mouth, alert ears and glistening eyes sure looks like a happy, grinning dog to me. And let's not forget that smiling tail.

So, I'd say smile, no; grin, yes.