When it talks about killing an animal verses killing a person, there is a difference here that is not really clear in this translation. If a man "beats an animal to death" (I think it implies another person's animal - correct me if I am wrong) he must make restitution for it ("You killed Joe's prized sheep, so, Ben, you have to give him your prized sheep") of equal value. A person who purposely kills (beats to death) another person is another matter entirely. Again, this has to do with the imago dei that I've noted before. Human life is precious, thus, GOD requires that the murderer's life be taken in recompense for the life that they stole.