The Tell-Tail Wag

By Michael Thal ~ Art by Tamara Petrosino

Your dog becomes excited when you arrive home from school. His body wiggles and his tail wags.

Your dog is telling you that he’s happy to see you. If you look closely, you may see that his tail is wagging farther to his right.

If he were afraid, his tail would wag farther to the left instead.

“Animals cannot tell us about their emotions, but dogs can wag their tails,” says Dr. Giorgio Vallortigara. He is one of the scientists who discovered the difference between “happy” tail wagging and “unhappy” tail wagging.

Scientists have studied the brains of animals and people for many years. They know that the brain has two halves—a right side and a left side.

The two sides do different jobs. For example, the right side of the brain controls the left side of the body. That means the left side of the brain controls the right side of the body.

In people, the left side of the brain also handles our feelings about things we like. It sparks our love for a parent and our feeling of safety under a warm blanket.

The right side of the brain handles our feelings about things we don’t like. It triggers fear, worry, and sadness.

Some animals’ brains also split these jobs between the right and left sides.

Many birds use the right eye to look for food and the left eye to watch for cats. That’s because the left side of its brain is in charge of feeding and the right side handles danger.

Dr. Vallortigara and two other scientists wanted to find out if a dog’s feelings affected how its tail wagged.

They designed a special box for the dogs, and put in one dog at a time. The dogs could see out only through a panel in one of the walls.

The researchers showed four things to each dog. First, the dog saw its owner. Second, the dog saw a stranger. Third, it saw a calm, relaxed cat.

Finally, the dog saw a big dog it had never seen before. The big dog was trained to act as if it wanted to be “the boss.”

When the dogs saw their owners, they all wagged their tails strongly. The tails swung far to the right most of the time. Their tails also swung to the right when they saw another person or a calm cat.

When the dogs in the box saw the mean-looking dog, their tails wagged farther to the left.

“The muscles in the right side of the tail show us his positive emotions,” says Dr. Vallortigara. “The muscles in the left side express negative feelings.”

Dr. Vallortigara thinks this knowledge will help veterinarians treat their patients. They’ll be able to tell what makes a dog happy and what doesn’t.