When a cat hisses, it is used a a defensive sound. The cat creates the hiss when she opens her mouth with lips pulled back, and then forces out a burst of air through an arched tongue. Since the sound resembles a snake, the cat will use the hiss to try and bluff her attacker into backing off.
Spitting will often accompany the hiss. The cat will produce the spit in reaction to being threatened or surprised. To add to the drama the cat may menacingly slap at the ground with her paw.
The hiss is used as a defensive warning. The cat is basically hoping that her vocalization and her accompanied body posture will deter any potential violence. If the danger persists, aggression will likely follow.
When a cat hisses i usually move in the opposite direction so my face doesn’t get slashed
Thanks Laurie, I think if we better understand why cats go into defensive postures we can lessen the stress that causes it.