Full body wag
You're probably familiar with this wag, which you likely see whenever you come home from work. Here, your pup welcomes you with tail wagging in a big circle. He'll also shake his entire body in a loose way accompanied by a submissive grin or a soft open mouth. If you notice a lot of swaying and wiggly motion closer to the head of the dog, the friendlier the dog is.
Fast and shaky
If you notice fast, vigorous and an almost shaking tail on a dog this is a sign of tension and/or hostility. This means that the dog can spring into action at any moment. This tail behavior indicates a highly aroused dog and should generally be avoided until it settles down.
This can almost be seen on its face: your dog seems to be contemplating his next move. A slow wagging tail may indicate a dog that is unfriendly, so proceed with caution and take the entire environment and personality of the dog into consideration. If it's an unknown dog, do not interact with it.
High and stiff
A high and stiff tail with fast wagging means that the dog is alert and aroused. He is confident and enthusiastic. If other dogs are near it could mean a display of dominance. If a high stiff tail is combined with any teeth, open mouth, raised hackles and a wrinkled nose, take it as a cue to back off, providing them with space to make them feel comfortable and confident.
Wagin' on the right
Research suggests that when a dog wags its tail on the right side, it's considered more likely to be friendly than when a dog wags its tail on the left side of its body. Researchers discovered that dogs tend to wag their tails on the right when they wanted to approach something, like their owner, but wagged their tails on the left when they were unsure of something.
A tail that is held at a low level, often covering the dog's anus, but not disappearing between the legs, indicates that he is not entirely comfortable with the situation he is in and could be feeling anxious, nervous or unsure. A tail wag or wiggle may also indicate a sign of appeasement.
This is slightly different from a pulled down tail. When the tail is between its legs, the dog is feeling threatened or fearful of the situation he is in.
Curled toward the head
Prior to deciphering what this cue means, there are a few things to take into consideration. Some tails are naturally curled or bend towards the head, so the dog could be relaxed. But if the tail is being held (or pulled) in the direction of the dog's head, it could indicate the dog is overstimulated, on high alert, or highly excited. It could indicate alarm or exaggerated joy, which is why watching the rest of the body language the dog is showing you is important to understand how the dog is feeling.
A dog's tail serves a purpose. It is an extension of its backbone with vertebrae and a sensitive part of a dog's anatomy that is prone to injury. So if a dog's tail cannot wag it can mean that the dog has an injury directly to the tail, or to other connected areas. A tail can be sprained, broken, dislocated or have never damage that may cause it to go limp. It's important to seek immediate veterinary care as damage to the tail can cause incontinence, balance issues and the inability to use the tail to communicate.
What about stubby tails?
Breeds with stubby or curly tails mimic the same signals as those with straight or long tails but do not do so in the same exaggerated way as those with longer tails. Notice the base of the tail for more cues.