Most dog owners know that like humans, dogs feel a range of emotions. Joy, fear, anger, sadness, anxiety, love, anticipation, surprise, jealousy, and loneliness are among those emotions that our best buds experience. But without the ability to develop a vocabulary, they need another way to communicate. So why do dogs wag their tails?


Why do dogs wag their tails?

“Dogs ‘talk’ with their tails. The position of the tail can tell us a lot about how a dog is feeling; hung low suggests fear and submission, whereas held high is a sign of dominance and arousal”, says Charlotte Corney, zookeeper and founder of The Wildheart Trust.

A wagging tail often conveys happiness and excitement, but neuroscientists at the University of Trento in Italy have found that the speed and direction of wag is also important.

The team found that when dogs are looking at something they want to approach, such as their owner, they wag their tails to the right. But when confronted with something they’d rather back away from, such as another dog displaying an aggressive posture, they wag their tail to the left.

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Of the positive responses (wagging their tail to the right), perhaps unsurprisingly, they also found that dogs wag their tails faster when greeted by their owner. They also found a medium, positive response was exhibited in dogs met by an unknown human, and a very low (but positive) response when greeted by a cat.

Understanding these behavioural asymmetries in tail wagging, could be beneficial to understanding your pooches positive or negative emotions, as brought on by different stimuli. In other words, it’s a non-invasive method to tell us what your dog likes and dislikes.

But it’s not just tail wagging that helps dogs convey emotion. According to a literature review carried out by veterinary researchers at the University of Bari, dogs have a behavioural repertoire when communicating with humans and other dogs. They have a vast range of visual, tactile, acoustic, and olfactory signals, that they use for expressive and fine-tuned communication. In lowering their tails, for example, they are attempting to reduce the appearance of their size and avoid conflicts with other dogs.

Your dog is saying something different depending on the direction they are wagging their tail. © Getty

Do dogs get tired wagging their tail?

Although they can exercise a certain amount of control, tail wagging in dogs is largely seen as an instinctive response to stimuli. You might remember a certain dachshund that made the news at the start of the pandemic, Rolo. He was so excited that his family were working from home during social distancing, that he sprained his tail from too much wagging. Thankfully, Rolo has since made a full recovery.

“Like all essential doggy business, such as breathing, barking and begging for treats, tail wagging uses energy. When a dog is happy, knows it, and really wants to show it, muscle cells in the tail produce the energy that is needed via a process called aerobic respiration,” explains Dr Helen Pilcher.

“This uses oxygen, but if the tail wags too much, and the muscles work really hard, the cells start to respire anaerobically, without oxygen. This generates less energy, and a by-product called lactic acid which causes temporary muscle fatigue and soreness. It’s enough to make even the most exuberant pooch take five and wait for its cellular batteries to recharge,” says Pilcher.

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A dogs tail poking out of the covers as he sleeps
Dogs who wag their tail in their sleep are probably dreaming. © Getty

Why do dogs wag their tail in their sleep?

Just like us, dogs go through sleep cycles of Rapid Eye Movement (REM) sleep and non-REM sleep. And it’s during REM sleep where they likely have the most vivid dreams. Yes, dogs dream – and if you’re wondering, what do dogs dream about, they’re probably dreaming about you.

Your pup’s nighttime adventures are likely made up of fragments from their real life. So, all that real-life tail wagging from car rides, walkies, dinner time, trips to the beach, and most importantly – when you come home from work, are likely being relived in doggie dreamland, resulting in happy, excited, or content tail wagging.


Sometimes dogs will wag their tails in their sleep for other reasons. If they’re experiencing anxiety, potentially from a nightmare, are cold or feeling submissive, this may result in a different type of tail wag. It’s often obvious when dogs are wagging their tail in their sleep for more unsatisfactory reasons, as it will usually be accompanied by other noticeable signs, such as shivering if cold, or whining if having a nightmare.

About our expert, Dr Helen Pilcher

Dr Pilcher is a science writer specialising in biology, medicine and quirky off-the-wall science. She's written many popular science books, and her latest book, Life Changing, How Humans are Altering Life on Earth (£10.99, Bloomsbury Publishing PLC) was shortlisted for the Wainwright Prize for Writing on Global Conservation, and is out now. 

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Holly SpannerStaff Writer, BBC Science Focus

Holly is the staff writer at BBC Science Focus, and specialises in astronomy. Before joining the team she was a geoenvironmental consultant and holds an MSc in Geoscience (distinction) from UCL.