An angry cat is probably fairly obvious to many a cat owner but it is important to know how to distinguish between a cat that is afraid and one that has become angry. A cat that is angry will puff out his fur, arch his back and spit, while a cat that is afraid will not puff up his fur or attack. Be aware that a cat can turn from being calm to afraid or angry in a matter of seconds. Know what play-fighting looks like. If you have more than one cat in the home, it’s important to be able to tell the difference between real aggression and mock fighting. Cats that are play-fighting may look violent but it’s all posture. Look closely (within reason); play-fighting cats don’t have their claws out and their bites are small and harmless. Source: wikihow