Sure, I’ll give it a shot.
The scene takes place in Bogart’s “Cafe’ Americain”. I’m going to assume you don’t know the movie or the characters, so here’s the rundown. Rick Blain (Bogie) runs a little cafe in Casablanca which is filled with people stuck in town awaiting mostly illegal visas.
At the beginning of the movie, we go through a little scene at the bar between Rick and his former girlfriend Yvonne. He sends her home with the bartender and she is not happy. The next night, she comes back on the arm of a German soldier. There is a short altercation at the bar between Yvonne, her German and a Frenchman who takes exception to Yvonne’s choice of date.
In the meantime, Rick’s true love, the one that broke his heart, has shown up with her husband. Ilsa (Ingrid Bergman) and Rick are plainly shocked to have ended up in the same place. Emotions and tensions are high.
Ilsa’s husband, Victor (Paul Henreid) is the leader of the Resistance. They are trying to get a visa out of Casablanca and stay out of the reach of the Gestapo, in this case personified by Major Strasser (Conrad Veidt), who is also at the cafe’.
The scene begins with several German soldiers singing something inflamatory in German. (I think it’s the Horst Wessal Song). Victor walks over to the band and tells them to play The Marsiesllais. They look at Rick, who nods.
The band and the customers drown out the Germans in a surge of freedom. Everyone sings, led by Victors strong voice. It’s thrilling, empowering. Casablanca is still Free France and everyone ther is going to make sure the Germans know it.
As the camera pans the cafe, we see that the female guitar player has joined in, the Germans have taken their seats in disgust and Yvonne is in tears, singing in a ragged, almost desperate voice.
It’s a hell of a scene. I believe it’s my choice as well.