German versionIn the German version, gore effects were removed and blood effects were toned down. Both differences only apply to human enemies. A detailed list of changes can be found on schnittberichte.com (German).
ReferencesIn the final level, after you get the last upgrade for the TMD, you can smash a vent in that very room, go down a ladder, and you'll find yourself at a narrow room, at the end of which there's a crack in the wall that lets in a bright light, and has a large donkey wheel wedged in. This is a clear wink at fans of the TV show Lost: A wheel, very much like this one down to the room it's located in and the way to access it, played a major part in the ending of season 4.
The entire thing can be seen in this video: http://www.youtube.com/watch?v=VdWxZy8NlBs
In the Xbox 360 version of the game you get an achievement for finding this.