We all know what a dog means when it wags its tail - it means they're happy, right? Well, maybe not according to leading animal psychologists who analyse what a dog may be or may not be feeling.  There may be more of a tale in the movements of a dog's tail than most of us think.

Most of us agree that it would probably make life whole lot easier and fun if dogs could actually converse rather than bark with us, but sadly they have not yet evolved to develop that skill. There are some obvious signs of what your pooch is thinking. For example, growling could show aggression, scratching at the door could mean a call of nature, and rolling on their backs could show submission.

However, in the opinions of experts like Stanley Coren, professor of psychology at the University of British Colombia, your canine companion may be trying to tell you much more with the movements and position of their tails. For example, a broad wag is a friendly sign and can mean that the dog is pleased.

If you see the tail drooping,it may be a sign that the animal is in a state of stress and anxiety. That's according to Josie F. Turner, a journalist specialised in animal welfare. This is especially obvious if there are whines coming from them, or they are trying to hide. It may be time to get them on the leash and take them for that precious 'w-word' – walkies. Most dog owners know never to say that word in the vicinity of their four-legged friend, or they will get overly excited forcing you to take them out.

A horizontal tail with slight movements may be a sign that your canine is nervous or uncomfortable. And the more ample the movements, the more nervous your pooch may be. Finally, an erect tail accompanied by a swagger in the hips and lots of movement is a sign that your dog is as happy as can be – and very alert. However, if the tail is straight up in the air with no movement, it could be a sign that your dog is alert and trying to exert dominance.

So, the next time you're greeted by a dog, make sure to have a look and see what their tail is doing. In their own way, they're trying to tell you if they're sad, nervous or happy. Many of us would like to know exactly what they're thinking. Maybe we should just be grateful their tails are wagging and they're not plotting our demise.