A cat's tail can act as a very good indicator of her moods and feelings. A happy, relaxed cat will hold her tail straight up; the higher the tail, generally speaking, the happier the cat. She will come to greet her owner or feline companion with her tail held high, often just bending over slightly at the tip.
A cat who is fearful or unsure will carry her tail half raised, and an unhappy cat will carry her tail low. A scared or angry cat may fluff her tail up to try to make herself appear larger and more threatening to adversaries. A cat's tail will twitch when she is excited or playful, and some cats may twitch their tails out of sheer pleasure when being petted.
If a cat is swishing her tail from side to side in broad movements, this can signal annoyance. If she does this when you are playing with her, you may wish to stop or she could follow up with a physical attack. A cat will lash her tail rapidly back and forth if she is really agitated or angry, and an attack may certainly be imminent, so be aware!
If a female cat crouches down, making treading movements with her back legs and holding her tail to one side, she is making a sexual invitation and is likely to be on heat.
A cat will hold her ears upright and forwards when relaxed and happy, or greeting her owner or other companion. If they are very upright, she may be alert and listening to something she finds exciting or intriguing.
An unhappy cat, however, will hold her ears back, indicating nervousness and possibly impending aggression. Twitching ears can also indicate a cat who is unsure about the situation in which she has found herself. A cat who's ears are flat back against her head is definitely feeling aggressive; it is thought that this posture offers the ears protection against attack or in a fight.
If her eyes are wide open, she is alert and interested. A cat who half closes her eyes is feeling sleepy and relaxed. If she takes a long and slow blink, this means that she is feeling very relaxed and content; a cat will communicate affection for her owner or feline companion by looking into the eyes, averting the gaze and slowly blinking. If you do this to her, she is likely to reciprocate the gesture.
Other body language
A cat will arch her back and bristle her fur when feeling threatened or aggressive, to try to appear as large and intimidating as possible to enemies.
A cat who is feeling totally relaxed and at ease will roll over onto her back and expose her belly- this is her way of showing that she has complete trust in you, as she is potentially exposing herself to attack. Be aware though that cats do not like having their bellies rubbed- do this and you are likely to feel her claws!
Cats will often greet a feline friend or owner by touching noses, or rubbing their faces along cheeks or ankles. As well as being a sign of affection, they have scent glands in their cheeks, so this action marks you with their scent as a sign of 'ownership'. You will probably see her marking items of furniture this way, to establish her 'territory'.
Cats will also lick each other in a sign of mutual grooming and affection. A cat will often lick her owner to show her affection. If you take time to study your cat's body language, you should get a much better understanding of how she is feeling.