A Dog Knows: Wagging Tails Are Not All Happy Tails
You think your Fido will greet the dog coming towards you with enthusiasm. After all, Fido's tail is wagging. Well, don't be so sure. That other dog - she knows better than you do.
Dogs, like humans, have brains with right and left hemispheres, and, as in humans, motor behaviors are controlled by opposite sides of the brains - that is, the right hemisphere is responsible for controlling movements on the left side of the body and the left hemisphere controls the right side of the body. Now, neuroscientists are looking into the roles both sides of the brain contribute to canine emotions.
Italian researchers, borrowing from earlier studies establishing that dogs wag their tails more to the right when happy and more to the left when nervous or upset, attempted to learn if other dogs can read those signs. They did this by showing videos to test dogs of other dogs wagging their tails, while other signs of their emotions were reduced by video manipulation. While the test dogs watched the videos, they were measured for heart rate and their outward behaviors observed.
Dogs that moved their tails predominantly to the right evoked almost no reaction from the test dogs. But the test dogs responded with more rapid heartbeats and more anxious behaviors when the dogs they were watching wagged their tails to the left, showing that dogs indeed can read tail signals from other dogs. Not only can they read them, but they read them in reverse, for example, the happy tail wagging dog is wagging to his right, but the test dog's left.
This diagram shows how the test dogs reacted to the tail wagging communication:
Whether or not you can analyze your dog's tail wags, take it from this study, another dog probably better understands how your dog is feeling when his tail wags.