Humans have long wondered what their dogs were trying to say with their tail wags, but now scientists believe they have interpreted that form of communication.

According to a press release, new research shows that a dog's brain operates similarly to a human's. Both are organized asymmetrically with right and left sides that operate differently. The researchers found that dogs can recognize and differentiate the meaning of a leftward wag and rightward wag.

"The direction of tail wagging does in fact matter, and it matters in a way that matches hemispheric activation," said Giorgio Vallortigara of the Center for Mind/Brain Sciences of the University of Trento.

The research team previously explored the same subject and found that right wags are associated with positive emotions, like seeing their owner. Left wags are meant to express negative feelings, like meeting an unfriendly dog. Also similar to humans is the association of the part of the brain to the action, meaning the left part of the brain activates a right tail wag and vice versa.

Expanding on their past work, the researchers examined how dogs reacted to another dog wagging its tail a certain way. When the dogs saw a video of another dog wagging its tail left, they appeared to tense up and show anxiety. When they saw a video of a rightward wagging dog tail, they remained calm.

"A dog looking to a dog wagging with a bias to the right side-and thus showing left-hemisphere activation as if it was experiencing some sort of positive/approach response-would also produce relaxed responses," Vallortigara said. "In contrast, a dog looking to a dog wagging with a bias to the left-and thus showing right-hemisphere activation as if it was experiencing some sort of negative/withdrawal response-would also produce anxious and targeting responses as well as increased cardiac frequency."

He said he does not believe this is a form of communication between dogs, but rather an association forged deep in their minds. It is an automatic reaction each dog has to certain tail wag and not a way for one to convey ill feelings to another.

"It could be that left/right directions of approach could be effectively used by vets during visits of the animals or that dummies could be used to exploit asymmetries of emotional responses," Vallortigara said. "That is amazing, I think."