Have you ever really thought this question? Why do dogs wag their tail? Most people would say that a dog wags its tail because it is happy, but most dog handling professionals would disagree. In much the same way as when humans interact with other humans, dogs use body language as a means of social interaction. A dogs tail is one of the most prominent body language features that they can use. The other reason is for their scent.
When people see a dog wagging its tail most people assume it is because the dog is happy. This is an all too common misconception and often leads to dog bites. One reason a dog will wag its tail is in anticipation. The anticipation can be for any number of reasons. For example, they can be anticipating a reward or confrontation. There are many more reasons, and with a little training most people can be taught to identify the different signals that dogs deliver. If a dog has its tail pointed up high and it is moving back and forth it means that they are in their happy place. It if is rigid with small movements from side to side it means that the dog is dominant and sending you a warning. If it is out flat they are being inquisitive. If it is between their legs they are often frightened. The tail is the best cue to a dogs intentions that you will encounter. If you watch dog attack videos in slow motion you will often see the tail wagging.
Why do dogs wag their tail for their scent?
Dogs do wag their tails for other reasons. You may have noticed dogs sniffing butts, even peoples. The reason dogs sniff butts is because dogs have anal scent glands. Each dogs anal scent gland gives of a unique smell, a smell that identifies that particular dog. A rather dominant dog will proudly wag its tail in an effort to move their scent around, while a less dominant dog will keep its tail tucked between its legs to keep the smell to itself, and hopefully fly under the radar.