It’s helpful to think of a cat’s tail as an indicator of its emotional state. While both dogs and cats “wag” their tails, felines’ movements are much more nuanced, thanks to a greater range of motion.
An upright tail indicates your feline is feeling friendly; a droopy tail tip indicates skepticism, while a twitchy, almost vibrating tail means extreme excitement. A tail positioned at a 45 degree angle can mean many things, and is usually a cat’s default state.
Aggression and fear are signified by a downwards-pointing tail, sometimes tucked between the legs. Watch for the dreaded “bottle brush” tail; an angry or scared cat often puffs up its tail fur to appear larger.