Tail Talk

According to www.k9puppydogs.com, your dog's tail has a language of its own. This site suggests that "The surer the dog is of itself, the more it moves its tail and says more things with it". 

Here is an interpretation, that this site suggests, of your dog's tail wagging.

• Relaxed tail: Relaxation and comfort.
• Hanging horizontal but not stiff: A sign of attention. The dog sees something interesting.
• Hanging horizontal but stiff: The dog is confronting an intruder or someone or something unknown.
• Upright tail: This is a sign of authority of a dog that shows itself dominant.
• Upright tail and turned over the back: shows trust and self-control.
• Downward and close to the hind legs: If its extremities are rigid and it wags its tail slightly, it shows "I'm not feeling well". If its legs are slightly bent it's a sign on insecurity.
• Tail hidden between its legs: Fear or submission.
• Raised tail and slow and rhythmic movement: The dog is on guard.
• Wagging lightly: Is their normal welcome.
• Wagging with broad circles: "I like you". When two dogs are mock fighting this movement confirms it's a game.
• Wagging at a slow speed: When it's being trained it means "I'm trying to understand you, I want to know what you're saying but I don't understand yet". Once it finally understands, the dog wags its tail faster.
• Short and slow movements: Shows that it's pleased. Sometimes its only wags its tail a few times when it's on the floor.
• Wagging fast: Excitement to a desired activity or object.

http://www.k9puppydogs.com/html/dog_s_tail.htm