Smiling?

I have an uncommonly sweet and docile toller. She loves strangers and will
pester them until she is pet.

The postman refuses to come to our door because he says she bared her teeth
at him. We dismissed him as a lunatic, but today she approached a stranger
and opened her mouth showing her teeth. She didn't curl her lips back or
anything, and was definitely friendly, but it did seem to be a display of
some sort. The guy she did it at says his dog also "smiles" at strangers.
If I didn't know better I might have thought it was hostile; so maybe the
postman wasn't a lunatic.

Is that a common diplay; opening the mouth to be friendly?


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