Today’s New York Times reports a study showing that dogs have right- and left-brained asymmetry as do humans and other mammals. Specifically, their left brains are the nurturing, loving, positive-feelings center. The right brain is associated with fear and depression.
And guess what? When a dog sees someone it likes, its tail wags predominately to its right (corresponding to the left brain). And when it encounters a menacing dog, its tail wags to the left (e.g. right brain).
This reminds me of a phenomenon in people’s faces: their expressions are not symmetrical, just as dogs’ tail wags aren’t. Cover up a photo of a person so that only one side of the face appears. Then switch the covered area. You’ll probably notice that the two sides don’t look the same at all. You can prove it also by photoshopping two left sides of faces together, and right sides. Even artists have known this–take a look at any Rembrandt portrait.
Ah, thereupon hangs a tale.