These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: Joyeux NoŽl
Actor Allusion: The French lieutenant compliments his German counterpart on his excellent French compared to his poor German. The German lieutenant responds "but your wife is not German." Guillaume Canet, the actor who played the French lieutenant, was married to the German actress (and a co-star in the film) Diane Kruger at this time.
Awesome Music: Phillipe Rombi's score, especially "I'm Dreaming of Home." Considering two of the main characters are opera singers this is kind of a given.
Fridge Horror: Lieutenant Horstmayer is Jewish. It is likely that his wife is too, along with being French. If he survives into the Nazi era... Let's just say that this may not be the last time he's thrown in a cattle car and sent to Eastern Europe.
The cat getting arrested for carrying a message between two sides. This incident was based on a true story, where the cat was shot for the deed.
Tearjerker: It's a war movie, people, about the Western Front. QED, it is sad.
The epitome might be in the ending, where as they are sent to certain death in Russia (for fraternizing with the enemy), the German soldiers are still singing the song the Scots taught them.
The instant the alarm goes off at the end of the movie and you realise who got shot.