Was just listening to some interviews, and the director's and producers were talking about how the monsters mutate and regenerate. They were talking about for, like example, say you are shooting the arm and it falls off. They can transform in a variety of ways. They could grow a lashing tentacle, or two arms, or another head, or the arm that fell off could mutate into it's own monster. They wanted to make these enemies extremely unpredictable and creepy. It really does sound very interesting.