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What's In a Wag?

by Jared Rigsby


If you own a dog,you’ve seen it all before. You  make your way home after a long day at work, and there's Fido waiting at the door, with his tail wagging a thousand miles an hour. You know he's thrilled to see you because, well, he's your dog, a best friend with a tail.

Happy dog in parkMost of us humans believe dogs wag their tails out of excitement, and that a tail-wagging dog is the sign of a happy dog.  But what if it actually signaled two polar-opposite feelings that actually appear alike?

Unfortunately, many dog bites occur because as often as not, humans don't recognize that the signal to back off is easily confused with exciting and seemingly welcoming tail-wagging, leaving a person dazed and confused at why the dog “suddenly snapped”. This often happens because of a misunderstanding between human and canine- you literally get your signals crossed. So how do we read what the tail tells?

Fortunately, science may have an answer. Researchers in Italy recently published the results of an experiment that suggests that dogs wag their tails in different directions according to their feelings. In other words, tail wagging isn’t always due to a happy or excited state of mind, but may instead be triggered by anxiety, or a sense of danger.  As it turns out, telling the two signals apart is actually quite simple- it's all based on which direction the tail wags.

The original experiment, led by Giorgio Vallortigara of the Center for Mind/Brain Sciences at the University of Trento in Northern Italy, presented four different tail “triggers” to a group of dogs. These tail triggers were a) the dog's owner, b)a cat, c) a dominant dog, and d) a stranger. So, when the dogs were presented with its owner, its tail would wag to the right (the dogs right).  On the other hand, when the dog was presented with another, more dominant dog, its tail would wag to the left.

Most people have heard about the difference in human brain hemispheres, divided between left and right, and how these hemispheres control different aspects of thinking. The left hemisphere controls intuitive, emotional thought, while the right hemisphere controls logical, analytical thinking.  On top of that, these hemispheres also control the opposite side of the body (i.e. the
left hemisphere controls the right side of the body and visa versa).  This concept of brain hemispheres controlling different aspects of thinking, and feeling, has been observed in dogs as Dog on green grasswell, especially though this tail wagging experiment.

When the dog's tail wags to the right, the left hemisphere of its brain is being used. This shows that for dogs, the left side of the brain is associated with positive feelings and social good will. This is the kind of tail wagging we all recognize as loving, more often than not.

On the flip side, a dog wagging its tail toward the left means that the right hemisphere has been activated.  The right hemisphere in a dog's brain associates the animal with anxiety, and the fight-or-flight instinct. This is the hemisphere that lights up when the dog is tense and uncomfortable, and biologically, prepares the animal to duke it out, or run for its life.

Though these different tail wags clearly communicate a message, researchers tell us that it‘s not done consciously. It's much like human facial expressions; when you laugh, you’re not trying to convey that you’re happy or something is funny, it just comes naturally. We all  inherently know what it means when another person laughs; it's just one of those things we just know. And the same is true for dogs wagging their tails, as the Italian researchers discovered in their next experiment.

This time, the Italian researchers found that dogs inherently recognize the meaning in the position of another dog’s tail, and understand the meaning of its movements. In this study, they showed videos of other dogs wagging their tails to 43 other dogs of varying breeds, When the dog on the video wagged its tail to the left, the dog watching the film not only appeared nervous, but also experienced an increased heart rate. The dog recognized the other dog's anxiety, purely by observing its tail movement.

Like humans, dogs are social beings, which is probably why we get along with them so well.  Early in our development, humans took the wolf, which had already developed an instinct to socialize, and bred it to socialize with us. As a result, the modern, domesticated dog has built in to its very DNA, the desire to respond well to humans. They bond with each other because both species have the ability to express themselves outwardly, and also to recognize those signals in others.

So here are some specific ways to recognize these signals, and thereby keeping both you and man’s best friend, safe and happy.....


A good place to begin is with the “stay away” signals. These are the signs a dog will offer to warn you that it may bite. Other than the previously mentioned leftward tail wag, a dog will position it's tail in one of three positions, to let you know it may not be cool with you. These signals indicate tension, aggression and fear.

2 tense dogs

1) When a dog is tense, it will likely hold its tail in a high, tight, stiff C curve over its back. It's similar to how humans “hold tension” in our shoulders, backs, and necks, causing muscles to tighten up. This doesn't mean the dog is a ticking time bomb of predatory aggression waiting to tear your arm off,  it may just mean he may need a little time to calm down or get used to you. Just relax and act like he isn't there, and eventually, he'll probably come closer to seek your attention on his own.

2) Unfortunately, some dogs can be aggressive or mean (don’t forget, they are predators after all). This is, more often than not, often due to mistreatment or bad parenting from a human. An aggressive dog will be obvious with its body posture, and its tail will be tense, moving back and forth slowly. This is known as “flagging”, and is the universal signal to keep your distance.

A frightened dog3) A frightened dog will hold its tail down, between its back legs. If it's deeply afraid, it may even tuck its tail up under its body. This is often a common and obvious signal, but doesn't necessarily mean the dog will bite. But it is possible a dog will lash out in a moment of fear, because fear causes a spike in adrenaline, which can put a dog in fight-or-flight mode. Like a tense dog, though, when it's given enough space and time, it will come back around.

4) On the other hand, a happy tail will make itself known.  If Fido's tail is wagging so hard it moves his rear around, then he is feeling extremely happy or playful. Happy tails can also be relaxed and slower moving, depending on the dogs personality or mood. The real key to recognizing a happy dog is in its over-all demeanor. Take time to recognize if a dog is stressed or tense and let him come to you, or at least give you a good sniff, before you attempt to put your giant human hands all over his head (which is attached to his mouth, to which is attached his great, big, sharp teeth.

5) Because tails come in all shapes and sizes, from long to nubby, it is very important to recognize some other aspects of a dog's body language. Some dogs hold their tails high and tight because of their breed, even when they are relaxed. So it's important to watch for changes in body position and tail movement when you approach any dog that isn't yours. If the owner is around, ask a few questions about his or her pet's personality before approaching it, such as ‘does your dog ever bite?’  Remember, each dog is an individual with a unique personality, so don't be afraid to explore and interact with them. Just remember to be careful.

So is it possible to tell the difference between friendly or hostile feelings in a dog who isn't already completely infatuated with you? The answer, my friends, is clearly yes. / Issue 155 - September 2018
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