I believe he's human. I think that they use the term "dog" like a absolutely obedient servant, if you get what I mean. They called Llewellyn "Dog no.7" so there must be other dogs, meaning he's not the only one and that adds up to him being human. For the needles and shots, I'm not quite sure yet but for now maybe it's either a shot with some kind of mad scientist substance or just a dose of something so he doesn't do anything bad?

So, Llewellyn is actually human or not? My thick skull can't comprehend some things.
It is mentioned that he's a creature which has gone through genetic mutations . It confused me when everyone in the prison saw him as Dog but not shavonne . Did they actually saw him as a Dog or they simply chose to see him as a dog? Can someone with peak sense of analysation enlighten me?