Does your dog wag left or right? It matters.

When your dog bounds towards you with his tail wagging furiously, you’d naturally assume he was pleased to see you.

Look closer, however, and that tail might be trying to tell you something very different. 

While all dog tails wag from side to side, it seems they do so with a certain left or right bias depending on the message your pet is trying to convey.

Dogs have different emotional responses to their peers depending on the direction of a tail wag, a new study found. Seeing a fellow dog swing its tail to the right keeps canines relaxed, while a wag to the left seems to induce stress, the researchers say.

For their study, a group of researchers recruited 43 pet dogs of various breeds. The animals were outfitted with vests that monitored their heart rate, and they were shown videos of other dogs wagging their tails either to the left or to the right. 

The pets that watched left-side tail wagging behaved more anxiously and their heart rate sped up, the researchers said, while the dogs that watched one of their peers wag their tail to the right stayed cool; they even began to approach the dog on the screen, suggesting they saw the right-side wagging as a signal of companionship, the researchers said.

But right-left tail wags may not be a form of secret dog language, the researchers say. They think the direction of tail wagging — and other dogs’ responses to it — might arise from automatic responses rooted in the different hemispheres of the canine brain.

Study leader Dr Giorgio Vallortigara, from the Centre for Mind/Brain Sciences at the University of Trento, said:

‘The direction of tail wagging does in fact matter, and it matters in a way that matches hemispheric activation.'

‘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, 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.’

Vallortigara and colleagues say understanding these responses might help improve dog welfare, and perhaps even help develop new strategies to keep them calm at the vet’s office.

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