Tails, Tails, Tails
Cats tails is all about balance. The balance in a cat is extremely important. Everyone knows that cats land on all fours, and how it lands on each paw one at a time, well, without a tail a cat would not be able to do that. A cat would also not be able to balance on a fence as well as it could with a tail. (it still could but it would be harder)
No no, this doesn't mean Bob tailed cats have no balance. A bob-tailed cat has no problem balancing, they just might be a little clumsy sometimes....sometimes.
A cat mostly shows it's emotions through it's Fur, Eyes, Ears, Snout, and Tail. Right now, we're just looking at the tail. This part is simple. If the tail is up, they could be saying hello, or be happy, straight backward, sorta on the edge, down could be aggitated or normal. The tail rapped around something could be protective to that thing, rapped around the paws could be normal or content, and tail tucked under the cat could be sleepy, or cold.