As it turns out, a cat’s tail does more than provide balance.Like dogs, cats use their tails to signal their moods and a form of talking to you and others.

According to Arden Moore, author of The Cat Behavior Answer Book (Storey, 2007) recognizing the messages delivered in tail talk can help you better communicate with your cat.

Flying high
A confident cat will hold their tail high in the air as she moves about her home/area. A tail that is erect like a flagpole signals a happy mood or greeting. Cats often send this message as they come close to a person of interest. If the top third of the tail twitches when the cat is around you, this means they adore you.

? mark
A tail looking bent in a question mark often conveys a playful mood. This would be a good time to engage in a five- or ten-minute play session.Feathers, cat-nip, toy ball, favorite toy or even your hands will do (watch for the claws if not de-clawed).

Flying low
A tail positioned straight down, parallel to the legs, can represent an aggressive mood. Be wary. That said, there are exceptions to this rule. Some breeds, such as Persions, Exotics, and Scottish Folds, normally tend to carry their tails lower than their backs. For those who own these breeds keep this in mind.

Tucked under

A tail curved beneath the body signals fear or submission. Something is making the cat nervous, upset or stressed.

Puffed up
A tail that's 3 times the normal size of a tail reflects a very upset or frightened cat. The cat is trying to look bigger to ward off danger.(Sometimes you'll notice a mohawk along their back as well).

Whipping
A tail that whips rapidly back and forth indicates both fear and aggression. It is a warning that says "keep away" or at a distance. Don't try to calm or sooth the cat. Let them come to you when they are ready.

Swishing
A tail that swishes slowly from side to side usually means the cat is focused on an object. Cats often swish their tails right before they pounce on a toy etc. It is part of their predatory poise.

Twitching
A tail that twitches just at the tip is a sign of curiosity and excitement.

Pal-to-Pal (cats)
A tail wrapped around another cat is equivalent to a person casually putting her arm around a favorite pal. It shows feline friendship.

There are many other ways that you cat pal expresses what they like or dislike etc. but I'd say the tail would be your best way to be able to tell what kind of mood a cats in. Just remember to pay attention to those little details and you'll have a great relationship with your feline friend.