Do dogs wag their tails when happy? Not always. An expert unpacks your pup's behavior.

Much like a facial expression, a dog wagging its tail can be a clue to a wide range of emotions. Though the popular imagination places dog-wagging squarely in the camp of happy emotions, the behavior can actually indicate all sorts of things — certainly not all positive.

Since human-canine communication has some road blocks, what our pets are trying to tell us is not always immediately clear.

To find out more about what a dog's wagging tail might mean, we consulted Dr. Camille Alander, a veterinarian with NYC's Bond Vet. Here's what she had to say:

Why do dogs wag their tails?

People often associate a dog wagging their tail with happiness Alander said, but that's not always the case.

The range of emotions that a dog can be expressing when wagging their tail is broad, she said. They might be excited or curious, even sometimes nervous or aggressive.

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Do dogs wag their tails when happy?

It depends. If a dog's tail is raised and flopping back and forth quickly that's generally a positive thing, Alander said, but if it's just standing straight up, that might indicate impending aggression.

If their tail is wagging back and forth but down between their legs rather than raised that's more likely to signal nerves, she said.

"Tail wags are kind of hard to read," Alander said, adding that there is some recent research suggesting that the different hemispheres of the brain may influence which direction the tail is wagging in. So when the tail is wagging to the right, these scientists believe that is positive, whereas if it's wagging to left, that's a negative indication (think left brain, right brain in humans.)

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This article originally appeared on USA TODAY: Why do dogs wags their tails? Here's what a veterinarian has to say