system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do wolves & dogs wag their tails when happy and hold them still when agitated, and why do cats wag their tails when agitated & hold them still when calm?
gpt
Different species use different ways of communicating their internal states (e.g. their feelings and emotions). Dogs and cats, while both domestic animals, share little else in common. They are not closely related evolutionarily and therefore it is quite logical that those groups or even species within those groups develop different ways of communicating with each other. Thus cats and dogs have different ways of communicating to us.