There's an old joke about a person who runs across a dog who was both barking and wagging his tail.

The punch line was the person "didn't know which end to believe." Although this was told as a joke, there's a lot of truth to it. It's not uncommon for a dog to both bark and wag his tail. Because despite what many people believe, a wagging tail does not always mean a happy dog. Tails come in a variety of shapes and sizes and have many different uses. One of the purposes is for communication. That is the use most people are aware of. Unfortunately, tail-wagging is often misinterpreted by humans. Dogs' eyes are sensitive to movement. A wagging tail gets a dog's attention and he instinctively know what the other dog is trying to tell him. Tail-wagging communication is much more complex than many people realize. The position of the tail, the speed of the wag, even the direction of the wag are all indications of what the wag means.

Position of the Tail

In talking about the position of the tail, it's important to realize that different dogs holds their tails naturally in different positions. Some dogs hold their tails slightly up. Some dogs' tails hang low. Others hold their tails slightly between their legs. Some breeds hold their tails curled up on their backs. And there are other breeds that hardly even have a tail at all. It's important that you be aware of how the dog holds its tail at rest when determining the position of the tail. If the dog is holding his tail vertically, it's an aggressive posture, wagging or not. You're being told to "back off." If the tail is horizontal, or in the dog's natural tail position, the dog is curious. If the tail is held very low, especially if it's tucked between his legs, he's being submissive.

Speed of the Wag

A slight wag of the tail is a tentative "hello." The dog is telling you he's not threatened, but he's not ready to be your best friend. Not yet, anyway. A wide, sweeping wag is saying what many people think all tail wags are saying. It's an expression of "I am not a threat to you," and can be a "happy" wag. A slow wag in a neutral position is a sign the dog is insecure and not sure how it should act. Tails that wag with very quick, slight movements—particularly if the tail is held high—are warning wags. They should be taken very seriously, since this could be a threatening posture.

Direction of the Wag

Surprisingly, there's even a meaning to the direction of the wag. When a dog sees a family member or anyone he's happy to see, his tail will wag to the right. However, if he sees a cat or an aggressive dog, his tail will wag to the left. Bear in mind, the dog will wag to his right if he's happy, so if you're facing him, he'll be wagging to your left. Remember that the tail is only part of a dog's body language. When you encounter a strange dog, pay attention to his entire body. If his muscles are stiff, his face is stiff, and/or his ears are flat back on his head or forward, he is not being friendly. But if the dog romps over to you with a sweeping tail wag, sits at your feet, and puts a front paw on your hand or your leg, he's asking to be petted. And it would be rude of you to refuse.