Reichu: This scene is a favorite target for people who like to read too much into NGE's Pointless Religious Symbolism™. In the evil AWL commentary, they mention something about the Eva "piercing the Angel's soul with a rib", and I recall seeing a thread somewhere where they read way too far into the whole thing. If overanalyzing anything in NGE is folly, it's the supposed religious symbolism!
tv33: How bad of an ass-kicking do you have to be going through to get beaten with your own rib? At this point, Sachiel should just walk away and cut his losses.
Reichu: Kind of hard to walk away when you have a pissed-off Eva sitting on you…