Almost everyone knows that if a dog is wagging its tail it's happy, right? Wrong. Being able to read what your furry friend is thinking and feeling takes more than a simple wag. 'A common misconception is that a dog wagging its tail is a happy dog, but that's not at all the case. It depends on a variety of things,' says Stanley Coren, psychology professor and neuropsychological researcher at the University of British Columbia, and specialist in the intelligence and mental abilities of dogs. Tail wagging, Coren says, can be broken down into the speed of the wag, size of the swing and elevation of the tail. For example, a dog that is not feeling well may wag its tail slowly, hold it very low and sway in small movements. Alternatively, when a tail is held very high and moving back and forth at a swift rate, the speed is usually due to excitement and happiness. However, the professor details another scenario: 'When the tail is high with short movements, the dog is basically saying, 'I'm the boss around here, so give me some space'.' He adds this latter tail wag is a warning to beware as the dog may be ready to snap at a hand or person. Another way of quickly assessing a dog's emotions is to see its tail as a thermometer with mercury that rises and falls - dominant tails are hot and high, while low tails are cold and frightened. A relaxed dog has a lightly drooping tail that isn't stiff. If you want to be sure your dog is happy, Coren says look for your dog's tail held moderately low with big swings that seem to drag the hip from side to side. 'This is the dog's 'you are my fearless leader tail wag' that shows he is very submissive. The dog is thinking you are my leader and you will not hurt me,' says the Vancouver-based professor, who wrote The Intelligence of Dogs. According to Coren, tail wagging is all about communication. He adds that studies show if a hungry dog is taken into a room, empty except for a bowl of food, it will show a tail with a minor excitement tremor. If there is a person in the room with the bowl of food, the dog will display its fearless tail wag. 'The dog won't wag without people around, the same way you won't walk into a room and say hello to a wall,' he says. A critical time to pay attention to your dog is when it's trying to assert its dominance. The professor says that when a dog's fur is 'roughed up and its tail is high, that is a very dangerous dog and you don't want to crowd it'. A dog under stress will show signs and symptoms that people tend to ignore, such as panting, a lowered body and wet footprints. 'It's a very common thing to see wet footprints during a dog obedience class because all the puppies are stressed,' says the author who also wrote What Do Dogs Know? and How Dogs Think: Understanding the Canine Mind. Besides the tail, the shape of your dog's mouth and subtle nuances can give a clue as to its state of mind. 'With a c-shaped mouth that is not showing too much gum and more teeth, this is a very dominant threat,' Coren explains. 'But if the mouth is open and you see gums and teeth, that's associated with fearfulness. This is actually more dangerous than a dominant threat because the dog is scared and thinking, 'you're scaring me and if you do anything more, I will fight back'.' Another major misconception is barking. 'Dogs usually bark in bursts of two or three barks with little space in between - that's a call-to-the-pack bark, meaning there is something going on and I think the pack ought to investigate,' he says. If you don't want to encourage your dog to bark more, it's best to ignore it and only reward silence, with praise or petting. Coren explains many people respond to barking in the wrong way by telling their dog to 'shut up', which to the dog, sounds like a bark. Therefore, the dog will think it's doing the right thing and continue barking. 'A lot of people seem to be very insensitive to small signals that are very important ... But you still need to take into account context and your dog's breed or breed mixture.'