What is a dog really saying with a tail wag?

What’s your dog really saying when it wags its tail? According to Italian researchers, dogs not only communicate happiness with a wag, but they also convey anxiety and potential danger. 

In a study published Thursday in the journal Current Biology, researchers described an experiment in which they observed the behavior and heart rate of 43 dogs of various breeds as they viewed a projected image of a dog wagging its tail.

When the videotaped dog wagged its tail toward the right side of its body, most of the dogs remained relaxed and calm.

However, when the videotaped dog wagged its tail toward the left side of its body, many of the live dogs appeared anxious, and experienced increased heart rates.

And when the video image of the dog didn’t wag its tail at all, the real dogs were only slightly less relaxed than whey they viewed the happy right-side tail wag, researchers said.

“The direction of tail wagging does in fact matter,” read a statement from Giorgio Vallortigara, a professor of neuroscience at the University of Trento, and director of the university’s Center for Mind/Brain Sciences. “That is amazing, I think.”

Vallortigara and colleagues wrote that this difference was evidence of hemispheric brain specialization, which is seen in many animals, including humans.

In these animals, the left and right brain hemispheres control and process functions on the opposite side of the animal. They are also associated with specific emotions and cognitive activities.

Therefore, a wag to the left suggests that the right side of the dog’s brain has been “activated,” researchers wrote. This right hemisphere is more closely associated with negative responses, anxiety and flight from danger.

In contrast, a wag to the right suggests that the dog’s left brain has been activated. This hemisphere is more closely related to positive responses and social approachability, according to study authors.

Interestingly, the study authors said their results were the exact opposite of those of a researcher who used a life-size robotic dog to test the response of real canines.

“It might well be that dogs simply did not perceive robotic tail movements as biologically convincing movements,” the authors wrote.

Vallortigara and colleagues Marcello Siniscalchi, Rita Lusito and Angelo Quaranta —  who all belong to the University of Bari Aldo Moro’s Department of Veterinary Medicine —  have conducted previous tail wagging studies.

In 2011, they published a paper in which they described the tail wagging of dogs that were presented with four stimuli: their owners, a cat, a dominant dog or an unfamiliar human.

When presented with their owners, the dogs were more likely to wag their tails vigorously to the right, whereas unfamiliar, dominant dogs were more likely to make them wag their tails to the left.

The most recent study was aimed at determining whether other dogs could interpret left or right tail wagging.

“It seems that one interpretation of these findings is that dogs might use tail-wagging direction as an indicator of the state of the other animal … and somehow match that state (emotional transfer) or use it as a signal of impending danger in the environment,” authors wrote.