It's simple; I guess you have seen fresh-made sword; after you hotted it, it's "glowing". Anub'Arak's "hands" should look similar. You simply have to take one of his "arms", make it glow red, and place it correctly, so that I can attach it to "hand,left" and "hand,right". There's a spell that makes his basic attacks heal him and deal extra chaos damage to the target (Lacerate), and that's supposed to be its effect.