(at around 1h 23 mins) Faraud, loading his pistol, drops a ball into the barrel and then rams it into place. When the ball drops,a metallic sound is heard, indicating that there is no powder in the barrel.
In the opening scene, Harvey Keitel's character's sword strikes home in the upper chest (near the heart) of his opponent, then the film cuts to a side view of the opponent depicting the sword as having entered his stomach area.
At the start all the soldiers wear side plaits in their hair. When Laura writes "Goodbye" on D'Hubert's sword, he walks in with no plaits. He then fights a duel with plaits and visits the general with plaits. In the next scene we hear "military fashions have changed" and everyone is without plaits.
When d'Hubert and the doctor discuss the ways of avoiding duels with Feraud, the doctor brings two bottles of wine. He hands d'Hubert a corkscrew, but d'Hubert leans back in his chair and starts stuffing his pipe. Yet literally two seconds later the doctor also sits down and picks up a glass from the table, where an opened bottle is standing. d'Hubert has also suddenly got a full glass.
During their second duel (in a cellar) one of their sabers scrapes against the stone wall and makes sparks. In the DVD commentary the director explains that this was done by taping an electrified wire mesh to the wall. The mesh is visible if you look closely.