Tail-wagging in dogs is the classic signal for happiness. But researchers have found that tail-wagging can mean that your dog is either happy or stressed. Activation of the left-brain causes a dog’s tail to wag to the right. Activation of the right-brain causes a wag to the left. That’s not new knowledge. Scientists detected that difference 6 years ago.
What is new is that, not surprisingly, other dogs can easily read the message your dog is sending with his tail. And so can you.
Researchers at the University of Trento in Italy tested 43 dogs of various breeds for their ability to distinguish between tail wags. They showed the dogs videos of other dogs wagging their tails (much like the one above) and monitored the dogs’ heart rates and reactions. How could they be sure that the dogs weren’t watching their canine buddies’ facial or body cues? The researchers also showed the dogs only a silhouetted version of a tail-wagging dog.
As it turned out, every dog responded the same way. Dogs watching other dogs wag their tails to the left looked anxious, and their heart rates increased. In other words, they, too, became stressed. But dogs watching others swing their tails to the right stayed calm and relaxed — an indication that right wags are an expression of companionship and confidence, according to these scientists.
Why study tail wags in dogs? The team said in the summary to their study, which was published in Current Biology in November 2013:
The finding that dogs are sensitive to the asymmetric tail expressions of other dogs supports the hypothesis of a link between brain asymmetry and social behavior and may prove useful to canine animal welfare theory and practice.
Bottom line: A dog wagging his tail to the right is happy, but a dog wagging to the left is stressed.