There's a method to the madness when it comes to dog's wagging their tails.
According to a study published in the journal Current Biology, dogs respond differently based on whether another dog wags its tail to the left or right.
The discovery suggests that, like humans, dogs' brains are asymmetrically organized, meaning the left and right side play different roles.
"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. "In other words, 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.
"In contrast," Vallortigara continued, "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. That is amazing, I think."
When the researchers showed dogs videos of other dogs wagging to the left, their heart rates picked up and they appeared anxious, but remained relaxed when they saw another dog wagging to the right.
According to the researchers, this suggests that the direction of tail wagging communicates something to the other dogs.
A previous study led by the same team found that dogs wag to the right upon experiencing positive emotions, and to the left when they felt negative emotions. All of this reflects what is going on in the dog's brain, since left-brain activation results in a wag to the right, and vice-versa.
Vallortigara isn't convinced that dogs are consciously trying to communicate their emotions, but that the phenomenon represents an automatic by-product of the activation of certain parts of the brain.
"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.