Dogs may be far more expressive and observant of other dogs than we previously thought.

I’ve often thought that if people were more like dogs, relationships between humans would be a lot less complicated. You’d know immediately if someone was truly happy to see you, just by the wagging of a backside. To us, it seems it’s hard to lie or hide your emotions when you have a tail.

It turns out, however, that not all wags are created equal. The direction a tail is wagging tells a tale far more nuanced than just whether or not a dog is happy. According to a new study published on October 31, 2013, in the journal Current Biology, canines that see the tails of other dogs wagging to the right feel relaxed, while dogs viewing others whose tails wag to the left makes them feel stressed.

Could this be a true form of intercanine communication, or is it purely mechanical—a byproduct of the activation of one side of a dog’s brain over the other?


A common myth is that a wagging tail means a friendly and happy dog. While it’s true that dogs do wag to express happiness, they also do it to show fear, insecurity or even to give a warning.

Reading the wags

While most owners tend to think that any wagging tail is a sign of happiness, that might not necessarily be true. Giorgio Vallortigara, a neuroscientist at the Center for Mind/Brain Sciences at the University of Trento in Italy and an author of the new study, says that dogs have different emotional responses to their peers depending on the direction of a tail wag. Dogs wag their tails to the right when they feel positive emotions, and they wag their tails to the left when they have negative feelings.

To conduct their study, the researchers created videos of dogs wagging their tails in a way that was designed to remove all other distractions, except the wagging tail. They then recruited 43 pet dogs of various breeds. The animals were outfitted with small vests that monitored their heart rates. Some of the dogs saw a video that showed a silhouette of a dog, while others saw an edited image of a real dog. In both cases, the only thing that moved in the image was the tail.

When the test-subject dogs saw the image of a dog with a tail wagging to the left, their heart rates picked up and they showed signs of anxiety. When the dogs saw images of dogs with tails wagging to the right, they stayed perfectly relaxed—some even approaching the dog on the screen, which suggests that they saw the right-side wagging as a signal of companionship.


Some researchers believe that watching dog tails may open a whole new window into a complicated dog communication system.

Vallortigara concluded that dogs, like humans, have asymmetrically organized brains. Left-brain activation produces a wag to the right, and vice versa. For example, a dog’s tail will wag to the right when seeing its owner come home, but it might wag to the left when confronting something it wants to back away from, such as another dog with an aggressive posture.

True communication or not?

The big question that remains to be answered is whether tail-wagging directional differences are a means for dogs to communicate with one another or whether they’re just physical, mechanistic behaviors, arising from automatic responses rooted in the different hemispheres of the canine brain.

While Vallortigara believes that directional tail-wagging is an accidental consequence based on which side of the brain has been activated, other researchers think that this study gives us a whole new window into a complicated dog communication system. While humans observe a simple tail wag and assume a dog is happy, dogs are able to perceive the type of tail wag and act accordingly.


The study should prompt researchers to look more carefully at predator/prey interactions.

Thomas Reimchen, an evolutionary biologist at the University of Victoria in Canada, believes this is one of the first studies to show that animals evaluate the left- or right-sided bias of other individuals and modify their behavior in response. He thinks the new study is a major contribution to our understanding of how animals interpret such signals and provides evidence that “docking,” or removing portions of a dog’s tail, compromises its ability to communicate. In addition, Reimchen points out that this study should prompt researchers to look more carefully at side biases in other interactions in the wild, such as those between predators and prey.

Whether or not you believe that dogs are truly communicating with each other by the direction their tails are wagging, this new information might help improve dog welfare and perhaps even aid in developing new strategies for keeping our pets calm at the veterinarian’s office.

And that makes me shake with happiness, all over.

Do you think dogs actually communicate by wagging their tails in a certain direction? Or are tail wags just automatic, physical reactions, a result of brain functioning?

Here’s to finding your true places and natural habitats,


If you would like to observe predator/prey interactions and some of the planet’s rare wild dogs, please take a look at our Africa safari tours.