In the second mission's third level, one room has a pair of Nazis recovering from a chase...
Nazi 1:phew ...I think we lost them...
Nazi 2: Oh, thank God.
Nazi 1: ...Hey, where are we?
Nazi 2: Hmm... I think we lost us too.
Several amusing safety notes can be found scattered around, particularly one describing a typo in the cablecar maintenance manualNote Instructions stipulating a weight tollerance which allowed for accuracy to be within five―hundred kilogrammes should have read five―hundred grammes! (that resulted in several deaths) and a stern warning not to brew coffee in the rocket-plane's fuel mixing system.
Return to Castle Wolfenstein has an amusing conversation with an exasperated driver trying to get a guard to let him enter the occupied village with a truckload of food for the General's mansion, mostly cases of cheese. It ends with him being refused, and the following:
Driver: "Then what am I supposed to do with all this cheese?"
At the start of the mission to infiltrate the missile base, there are some german soldiers near from your starting position who noticed your supplies were dropped near to their position, whose Allied origins would give away the whole stealth mission. They are argueing if they should investigate, but decide against it, thinking they might have been part of an excersize by nearby stationed Fallschirmjägers. And just like that, you've received a bit of foreshadowing of what you can expect later in the mission, revealling the other elite unit that's in this area.
One of the soldiers is listening to a broken record playing Beethoven's 'Fur Elise' as well.