Despite the grim subject throughout the film, in an interview on the second disc of the Criterion Collection box set, actress Hélène Surgère claimed the mood was actually rather jovial on the set. She said the abundance of teenagers who had never acted before led the mood to be happy and at times, even fun, with the cast often playing practical jokes on each other. She also said that the movie was literally "made" in the editing room and the filmmakers had no idea how grim a movie it was until they saw the finished product at the premiere.
The Duke: [singing]
On the bridge of Perati, there flies a black flag, the mourning of the Julian regiment that goes to war. On the bridge of Perati, there flies a black flag. The best young men lie under the earth.