Critical Research Failure: The original manual for Castle Wolfenstein describes the firearm that the player is given at the start as a "Mauser M-98 pistol fully loaded with ten bullets". The real-life Mauser M-98 was a bolt-action rifle with a five-bullet magazine (ironically, no rifles are seen in the entire game). It is possible that the game developers confused it with the C96 (a Mauser pistol with a 10-bullet magazine). But by World War II, even that gun was largely discontinued by the Germans in favor of the Mauser HSC, Walther P38, and Luger P08 (all of which had eight-bullet magazines).
Most Annoying Sound: "HALT! AUSPASS!" A whole generation of middle school students learned the hard way that you can't play Castle Wolfenstein on a computer in the library unless you got a hacked version that disabled the sound.