Anytime the hairs fluff out, a cat is trying to make itself look larger and therefore more of a threat and not to be messed with. The hackles along the spine raise up when a cat has been suddenly frightened, perhaps by a loud sound or a threatening predator nearby. Of course, the ears and the face of a cat can show a lot of emotion. Ears facing forward simply show the cat is paying attention to something in his surroundings. Accompanied with facial expressions, especially the eyes, and you can see a lot of what your cat is thinking.
Posture also plays a part in cat language.
The arched back is something we all recognize from the Halloween traditions. But some poses show subtle attitude changes. A cat lying on his side is more relaxed than one lying down with his paws tucked under. Most of us can recognize play in the body language of our cats. Understanding our cats' methods of communication is the first step in understanding them and in communicating with them.