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A puppy's tail wagging on the left side of their body might mean something profoundly different than wagging on the right side.

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As cute as it would be, dogs can’t talk, and their faces aren’t as expressive as ours, so it’s sometimes hard to tell what they’re thinking.

But dogs do communicate in one way we can’t: with their tails. Those fluffy tails are constantly conveying your dog’s mood, but just because they're wagging it all over the place doesn’t always mean your dog is excited to see you.

A tail wag doesn’t always signal happiness and friendliness. It’s way more complicated than that. The exact behavior can vary depending on the breed of dog, but the general pattern is the same.

If your dog lowers their tail between their legs, it probably means they’re scared, anxious, or submissive. If they hold it up, something has captured their interest, like a squirrel! The higher the tail, the more excited the dog is feeling, although the relative height varies between breeds.

Some dogs just naturally hold their tails higher than others. If their tail wags slowly, your dog is maybe a little uncertain about the situation. But if it’s waving energetically from side to side, it’s probably exactly what you think: a happy, enthusiastic hello.

As strange as it sounds, a pair of studies by a group of Italian researchers showed that which direction a dog wags its tail is important, too. In the first experiment, 30 dogs were exposed to four different stimuli: their owners, strange humans, a dominant unfamiliar dog, and a cat. The dogs wagged their tails much more on the right side of their bodies when they saw their owner, and slightly more on the right when they saw a strange human.

They also tended to wag on the right when they saw a cat, but the movements were smaller and more insecure. But when they saw a dominant, strange dog, they wagged more on the left side of their bodies. According to the scientists, this means they wagged on the right when they saw things they’d like to approach, and on the left when they saw things they’d want to avoid.

See, the two sides of dogs’ brains have different specialties. The researchers suggested that one side handles approach responses, like when a dog greets its owner, and the other side handles withdraw responses. And which way the tail waved seemed to depend on which half of the brain was being activated.

A followup study with about 40 dogs showed that other dogs could actually pick up on this. When they saw a video of another dog wagging its tail on the left, they got anxious, and their heart rates went up. But when they watched a video of a dog wagging its tail on the right, they stayed relaxed.

It’s possible that this is a way dogs communicate with each other, since many of them have easily visible tails. So if you want to become an expert dog whisperer, keep a close eye on that tail. It could be telling you more than you’ve ever realized!

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