40 Knives is a Nazi Zombies related trophy/achievement worth 25G and a Bronze trophy on PS3. It is available in Call of Duty: World at War. A player can get this trophy/achievement by killing 40 zombies with the Bowie knife. This trophy/achievement is only available on Der Riese as that is the only place one can find the Bowie knife. A strategy that could be used is to wait until insta-kill is on and run around stabbing the zombies. Remember that the Bowie Knife is a one hit kill until round 11.