I just wanted to post my undertanding of cats' different forms of communication... and I'm hoping people will post their ideas and correct me wherever I'm wrong about something...
meowing - "I want something" (food, attention, etc.)
hissing - a warning or threat ("leave me alone or else"), anger, aggression
growling - like hissing, but seems to be more a show of irritation than a threat
swishing tail - excitement, but not necessarily a happy excitement - sometimes it is more of a nervous excitement
peeing on things - marking territory
pooping outside of litterbox - I'm not sure
scratching - exercise or stress relief
Feel free to add to the list...
meowing - "I want something" (food, attention, etc.)
hissing - a warning or threat ("leave me alone or else"), anger, aggression
growling - like hissing, but seems to be more a show of irritation than a threat
swishing tail - excitement, but not necessarily a happy excitement - sometimes it is more of a nervous excitement
peeing on things - marking territory
pooping outside of litterbox - I'm not sure
scratching - exercise or stress relief
Feel free to add to the list...