Could any animal potentially be a companion/ guide to the Avatar?
I'm sorry if this is a really stupid question, but I'm only just rewatching ATLA after a few years, and I've forgotten a lot of details, and I cant be bothered to wait for my answer by just watching, I'm impatient and might miss it.
But I'm basically wondering if any animal in the entire world could serve as a companion/ guide to the Avatar, or are there certain rules, like does the animal have to be intelligent or strong, because I don't think an ant would be a companion at all, because, if I'm remembering correctly, isn't the Avatar and their companion life-linked, so if one died the other would, too. So I would assume the companion would have to be strong enough to not die easily.
Also, would the companion have to be an Animal relating to the Avatar's birth element? Like how Aang had his Air Bison(air), and Korra with her Polarbear Dog(water).
I apologize if this has been asked before, but I couldn't really find anything on this.