Cats are wonderfully communicative animals. They can make over 100 vocal sounds -- ten times more than dogs. They also communicate extensively through their tail movements. Cat owners can get a good gauge on their cat's emotions by understanding the various tail signs:
1. Tail curves gently down and then up again at the tip: This is a relaxed cat at peace with the world.
2. Tail raised slightly and softly curved: Cat is getting interested in something.
3. Tail held erect but with the tip tilted over: Cat is very interested and is in a friendly, greeting mood, with slight reservations
4. Tail fully erect with the tip stiffly vertical: Intense greeting with no reservations. For adult cats this is borrowed from the action of a kitten greeting its mother. The kitten's signal is an invitation to the mother cat to inspect its rear end.
5. Tail lowered fully and possibly tucked between hind legs: Signal of defeat to totally submissive cat showing its lowly social status.
6. Tail lowered and fluffed out: Cat is indicating active fear.
7. Tail swished violently from side to side: This conflict signal of tail wagging is its most angry version. If the tail is swinging vigorously from side to side, it usually means that the cat is about to attack.
8. Tail held still, but with tip twitching: This version of tail wagging shows only mild irritation. If the tip twitches become more powerful, then it is a clue that a swipe from a bad tempered paw is imminent.
9. Tail held erect with its whole length quivered: Gentle quivering action often seen after a cat has been greeted by its owner. The same action is observed when urine spraying is taking place outdoors, but in this case no urine is produced. The gesture appears to have meaning of a "personal identification" as if saying "Yes, this is me!"
10. Tail held to one side: Sexual invitation of a female cat in heat. When she is ready to be mounted by the male, she conspicuously moves her tail to one side. When the tomcat sees this he knows he can mount without being attacked.
11. Tail held straight and fully bristled: Signal of an aggressive cat.
12. Tail arched and bristled: Signal of a defensive cat and one that may attack if provoked further. Bristling fur makes the cat look bigger and may deter the enemy if the defensive cat is lucky.
Article courtesy of: Petsmart.com