James
I know what it looks like, but I promise that's not what I'm doing.
I'm pushing his buttons. He's already predictable, and the more annoyed and irritated he becomes, more likely he is to slip up. He won't kill them. There's no reward in that for him. The possibility that he could, the fear that causes for the rest of us, the feeling that we don't have any control over the situation? That's what he's eating up here.
Just look at his conversation with Lyra, the way he's trying to edge Bruce into rage.