What Is a Dog Thinking
When It Wags?
by a wagging tail
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Read the transcript
The full narration of the video.
A dog wagging to the left may not be happy at all. When you walk in, its tail is a blur, and it looks the same on both sides. But scientists filmed the wagging and measured the angle frame by frame. The tail often leans to one side.
Left and right here mean the dog's own left and right. Stand behind it, and you won't mix them up. Seeing its owner, a dog swings its tail more to the right. Seeing a strange, stern-looking dog, it swings more to the left. Can other dogs see that small lean? Scientists tested it with videos.
A screen shows a dog wagging its tail. The watching dog wears a little vest that tracks its heartbeat. When the tail on screen leans right, the watcher stays relaxed. When it leans left, the watcher's heart speeds up. Some tuck their tails. Some back away.
So between dogs, which way the tail leans is a message they can read. It's a bit like a car's turn signal. When the car ahead blinks, the driver behind knows where it's going. A tail leaning right says: I want to come closer. Leaning left says: I want to get away.
Why does it lean? A dog's brain has two halves, and each controls the opposite side of the body. Scientists think that when a dog wants to approach, the left half of the brain works harder, so the tail swings a bit more to the right. When it wants to back off, the right half works harder, and the tail swings more to the left.
A driver flips the turn signal on purpose. The dog probably doesn't choose its lean. Its body just gives it away. So what is a wag itself saying? Most often: I'm stirred up, and I want to deal with you. Happy is one kind of stirred up. Nervous is another. The lean is small and hard to spot at a glance. Read the whole dog: how high the tail is, how loose the body is, whether the hips wiggle too.
The evidence is still thin. One team tried a robot dog in a park, and got the opposite result. So a tail tells you more than happy or not. It tells you whether the dog wants to come over or walk away. Take a guess: when you walk in, which way does your dog's tail lean?
One tail,
often leaning
When you walk in, the tail is a blur and looks the same on both sides. But scientists filmed wagging dogs and measured the angle frame by frame. The tail often leans to one side.
Left and right here mean the dog's own left and right. Stand behind it and you won't mix them up.
Owner: right.
Stern dog: left.
Same dog, same tail. What changes is who is in front of it.
Other dogs
can read the lean
Scientists showed dogs videos of another dog wagging. The watching dog wore a little vest that tracked its heartbeat.
When the tail on screen leaned right, the watcher stayed relaxed. When it leaned left, the watcher's heart sped up. Some tucked their tails, some backed away.
Between dogs, the lean of a tail is a message they can read.
Like a car's
turn signal
When the car ahead blinks, the driver behind knows where it's going. A tail leaning right says "I want to come closer." Leaning left says "I want to get away."
One difference: a driver flips the signal on purpose. The dog probably doesn't choose its lean. Its body just gives it away.
Where the lean
comes from
A dog's brain has two halves, and each controls the opposite side of the body. Scientists think that when a dog wants to approach, the left half works harder, so the tail swings a bit more to the right. When it wants to back off, the right half works harder, and the tail swings more to the left.
This is the current best guess, not a settled fact.
The wag itself:
stirred up
Most often a wag means: I'm stirred up, and I want to deal with you. Happy is one kind of stirred up. Nervous is another.
The lean is small and hard to spot at a glance. Read the whole dog: how high the tail is, how loose the body is, whether the hips wiggle too (tail height is covered in who the wag is for; why dogs wag more than wolves in this one; mouths in the dog grin).
The evidence
is still thin
Another team tried a robot dog in a park. When its tail wagged left, more dogs walked right up without stopping, the opposite of the video study. The two experiments were done differently, so they are hard to compare.
Quick check
When a dog sees a stern stranger dog, which way does its tail tend to lean?
Like a turn signal: leaning right says "I want to come closer," leaning left says "I want to get away."
