A recent article by David Youngblood argues that the La Marseillaise scene in Casablanca is the single greatest scene in cinema history. I don't know enough film history to agree or disagree, but Youngblood's explanation has significant implications for structuring advocacy techniques well beyond the movies. He emphasizes the importance of the "turning point," in which the meaning and direction of the story become clear. As Youngblood puts it:
The scene marks a major turning point in the film. Directly preceding this scene, the bar owner Rick (Humphrey Bogart) refuses to give or sell letters of transit to the war hero/revolutionary Victor Laszlo (Paul Heinreid). The letters of transit are the only hope of freedom for Victor, and his only chance at returning to his efforts at insurgency against the Nazis; Rick knows this, but is still too hurt and bitter that his lost love Ilsa (Ingrid Bergman) has chosen Victor over him. Rick’s refusal is essentially a Nazi victory, despite his careful attempts at framing his (in)actions as simple neutrality. The Germans, led by Major Strausser (Conrad Veidt), have established a de facto control over Casablanca, acting through the openly self-interested French Captain Louis Renault (Claude Rains).
After “La Marseillaise,” everything changes. The uneasy stalemate between Victor Laszlo and Major Strausser can no longer continue in the face of such open defiance of German power. Strausser orders Renault to find a pretense to shut down Rick’s — leading to arguably the film’s best exchange of dialogue. Strausser uses Ilsa to increase the pressure on Victor. Everything kicks into gear, as now Rick, Ilsa, Victor, and Louis are all forced into unpleasant decisions that will push the film toward its climax.
Litigators often recognize the potential importance of a key fact or a revealing instance that makes everything else fall into place. For Youngblood, that happens in Casablanca when Victor Laszlo shows the courage to confront the Nazis in Rick's Cafe.
You can read the full review here, with a moment-by-moment breakdown of the characters' reactions.
Here is the scene: