You can tell a great deal about your cat’s mood by looking at his tail, but contrary to what a lot of people think, a fluffed up tail does not always represent fear and aggression in a cat.
When my cat is in an ultra lively mood, she will sometimes run madly around near me, as if she is trying to catch something. When I turn around to see what she is doing, I notice her stood still right next to me, her eyes all wide with her tail upright and fluffed up like a feather duster. I can, however tell by her body language that she is in the mood for play not fighting and it is usually the cue for me to bring out a piece of string, or find a nice strong branch in the garden for her to chase after.
When a cat is in direct confrontation with another cat you may notice his tail fluffing up, as well as the fur all over his body. What he is in fact trying to do is make himself appear bigger and stronger than his opponent. He will probably be standing upright and looking dominant.
When he is ready to “go into battle” with his opponent, his upright bristled tail will slowly move into an arched position, and he may start making a low growling noise. If you ever see your cat adopting this aggressive stance in front of another cat, the very last thing you should do is pick him up in order to prevent the impending fight. His opponent will almost certainly run away as soon as you intervene, but your cat will still be well and truly in attack mode for a few minutes afterwards. If he is in your arms whilst he is in this frame of mind, it is very likely he will direct his aggression at you.
Alternatively if you notice your cat in close proximity to another cat, crouched down with his ears flattened and a downward pointing fluffed up tail this indicates he is frightened. It could also suggest that he is trying to avoid any further aggression.
Even though a fluffed up tail can represent a range of emotions in a cat, it is quite easy to determine your cat’s mood by also observing his general demeanor and body language. As a general rule, if a cat has a fluffed up tail when in close proximity to another cat, you can almost guarantee he is not in the mood for cuddles!