Animal Behavior
 
 
Tale of the Tail
While dogs primarily communicate with their tails using various forms of wagging, cats communicate with their tails more in terms of position and shape. The position we're most familiar with is the straight up "greeting." The tail is vertical like a pencil, and you usually see it when your cat is happy to see you. If the tip of the tail is bent slightly, it generally means he's very happy.
A tail straight up with the fur bristled out has quite the opposite meaning. This cat feels threatened. Usually when the cat is in this mode, she'll stand sideways to the perpetrator in order to appear as large as possible.

A cat often uses her tail to let you know her intentions in order to avoid conflict. A cat who is being petted, and decides she no longer likes it, will begin a slow swish of the tail. The cat is telling you to back off. If the unwanted petting continues, most cats will either bat you with a front paw or get up and walk away, disgusted.
A cat that has really had it with the person or animal annoying her, will whip her tail rapidly. If that's not enough for the annoyer to get a clue, there's usually a deep growl to accompany the frantic tail. The cat has given more than fair warning, before becoming aggressive.
When stalking prey (real or imagined) the cat's tail will be straight out, twitching or quivering. This is usually seen when the cat's whole body is spring-loaded, in pre-pounce position. The subtle movement of the tail is to notify other cats of their intentions, while not alerting their prey.
 
 
Cat Tail Dictionary
 
Straight Up: Hey, how's it going?
Straight up, Tip Bent: Great to see you! Is that food I smell?
Straight Up, Fur Bristled: You're scaring me.
Twitching: Get ready for the master hunter.
Swishing: Back off!
Whipping: I'm warning you!
Straight Out, Still: I'm focused on something.
Straight Out, Twitching: I found what I want. Prepare for attack!
Hooked (Upside Down U), with Other Cats: I'm playing!
Lowered: I submit.
Wrapped around Body: I'm fine with things as they are.