The average person can probably figure out that the movie is a metaphor for America joining the War. It's re-examining little details in the movie where the brilliance kicks in. Case in point; the famous scene where Rick grouses that, over in America, people are "asleep." He means it both literally, due to time differences, and metaphorically, due to their unwillingness to oppose Axis tyranny and determination to stay out of the conflict.
Rick being America personified adds new meaning to the last thing Ilsa says to him: "God bless you." ("God bless America.")
One for Peter Lorre fans. Ugarte fires four shots while trying to escape the police. Most handguns (in movies at least) contain six bullets. He already used two bullets on the two Nazi couriers.
The "La Marseillaise" scene becomes even more brilliant if you know that "Die Wacht am Rhein", the song the German officers were singing, had origins rooted in the historical French-German enmity.
It's well-known that the scene was a Shout-Out to a similar scene involving those songs in The Grand Illusion, but since Casablanca was set in the present day, it's possible that the characters had all seen The Grand Illusion (which had been a major hit in France) and were deliberately re-enacting it. (Of course, with Marcel Dalio in both films, that opens up a Celebrity Paradox).
Real Life Writes the Plot: Producer Hal Wallis wanted to use the "Horst Wessel Song," the official Nazi anthem, but could not because when production began, it was still protected by copyright!
Also, there's the fact that the Germans are playing the song on not just any piano, but Sam's piano, and almost certainly didn't ask Sam himself nicely about giving up his seat. Rick's decision to back up Victor is as much a personal reaction to the Germans snubbing his friend and business partner (and him by association, since it's Rick's cafe) as a display of sympathy for the refugees.
And it would be particularly galling for a French patriot to hear that song sung by Nazis occupying France, since the lyrics refer to defending the Rhine from foreign invasion - i.e., France invading Germany. ("Die Wacht am Rhein" means "The Watch on the Rhine.") "La Marseillaise" happens to be a tremendous retort, as its original name was "Battle Hymn for the Army of the Rhine."
When Renault says they can't decide whether Ugarte committed suicide or died trying to escape, it's possible he was being serious. After all, Suicide by Cop is a real method for people who don't want to be in jail, but aren't willing to take their own lives. It's possible Ugarte knew he would die if he tried to escape and preferred that to being in the custody of the Nazis.
Annina Brandel (the girl from Bulgaria trying to get exit visas from Louis) calls her new husband Jan "such a boy" as she frets about what he'd think if he knew what she might have to do with Louis to get them. We see how right she is about her husband's naivete when he tries to pay Louis his bribe money at the cafe in front of everyone.
