Heavy Reader

Kill a Librarian - the huge ape-like beasts in the Library levels. They're tough and normally you're meant to back away slowly (they only attack if you run or break eye contact). To kill one you'll want serious firepower: unload a heavy weapon (the Abzats/heavy shotgun or plenty of military-grade rounds) into it, ideally while backpedalling, or bait it and hit it hard. Bring ammo - they soak a lot.