How Many Tail-signals Does A Cat Make?

In addition to the familiar tail-wagging of a cat in conflict, there are a number of other tail-signals that indicate its changing moods of the pet feline as it goes about its business. Each tail movement or posture tells us (and other cats) something about the animal's emotional condition and it is possible to draw up a "de-coding key", as follows:

Tail curves gently down and then up again at the tip:
This is the relaxed cat, at peace with the world.

Tail raised slightly and softly curved:
The cat is becoming interested in something.

Tail held erect but with the tip tilted over:
The cat is very interested and is in a friendly, greeting mood, but with slight reservations. 

Tail fully erect with the tip slightly vertical:
An intense greeting display with no reservations. In adult cats, this posture is "borrowed" from the action of the kitten greeting its mother. The kitten's signal is an invitation to the mother cat to inspect its rear end, so there is an element of subordination in this display, as there is in greeting ceremonies. Tail lowered fully and possibly even tucked between the hind legs:
This is the signal of a defeated or totally submissive cat that wishes to stress its lowly status.

Tail lowered and fluffed out:
The cat is indicating active fear. 

Tail swished violently from side to side:
This is the conflict signal of tail-wagging; in its most angry version. If the tail swings very vigorously from side-to-side it usually means that the animal is about to attack, if it can summon up that last bit of aggression. 

Tail held still, but with tip twitching:
This is the version of tail-wagging that indicates only mild irritation. But if the tip switching becomes more powerful, then it can act as a clue that a swipe from a bad-tempered paw is imminent.

Tail held level with its whole length quivered:
This gentle quivering action is often seen after a cat has been greeted by its owner. It is the same action that is observed when urine-spraying is taking place out of doors, but in this case there is no urine produced. Whether some slight, invisible scent is expelled is not clear, but the gesture appears to have the meaning of a friendly "personal identification" as if the sat is saying, "Yes, this is me!".

Tail held to one side:
This is the sexual invitation signal of the female cat in heat. When she is ready to be mounted by the male she conspicuously moves her tail over t one side. When he see this, the tom-cat knows he can mount her without being attacked.

Tail held straight and fully bristled:
This is the signal of an aggressive cat.

Tail arched and bristled:
This is the signal of a defensive cat, but one that may attack if provoked further. The bristling of the fur makes the animal look bigger, a "transformation display" that may deter the enemy if the defensive cat is lucky.