Interesting post, dear friend. I think we humans felt the need to give a name to the dark side of us since the very ancient time. Folklore and religions give different name to the evil and I have some thought about it: without an evil, we couldn't know what's the not-evil; if there's an evil, it's not our fault, right? The wrong/horrible things that happens are cause the evil. Personally, I think we can call that dark side of the humans using different names, but it's always part of us :( About pets, I think they feel the humans better than us, they know when a person is dangerous or not ^_^