I talk to pets that I know I'll get a response from, or ones that know at least partially what I'm on about. I'm talking about dogs here.
An example I like is my dog called Milly. She know's her name. Or the sound at least. I can say "milly!" and she'll look. I can also say "pilly!" or "quilly!" and she'll still look. She knows the "illy" sound means.. her.
With a cat, I'm not sure they know their name, never mind any other words. You get absolutely nothing back from a cat. That's why I wouldn't speak to them. They'd just stare into your soul and not so much as flinch, before shutting their eyes and going to sleep while you're mid sentence!