This film is based on a British novel of the 1930s written by the poet C. Day Lewis (under the pseudonym "Nicholas Blake") and is one of several novels by him to feature as its hero the brilliant amateur sleuth Nigel Strangeways. This adaptation, in addition to moving the action to modern-day France, entirely leaves out this leading character (or any new French character equivalent to him).
The role of Paul Decourt was first proposed to Philippe Noiret, but he refused, especially because he dreaded the boat scenes. When Claude Chabrol proposed the role to Jean Yanne, the latter answered him: "I do not see any objection".
The title of Cecil Day-Lewis's novel, "The Beast Must Die," and thus the title of the film "Que la bête meure" is inspired by a passage from Ecclesiastes 3:19 of the Bible: "For the fate of the sons of men and the fate of beasts is the same. As one dies so dies the other; indeed, they all have the same breath and there is no advantage for man over beast, for all is vanity."
The only film in the 'Hélène cycle' where Claude Chabrol's regular leading actress in the cycle, Stéphane Audran, doesn't star as a character named Hélène. Caroline Cellier plays the role of a character named Hélène instead.
When Paul's wife talks to Charles about the "Nouveau Roman", she mentions several writers, including Paul Gégauff, who is credited in this movie for the screenplay and dialogue. She also mentions "Monsieur Robbe-Grillet" - Alain Robbe-Grillet, a writer (and occasional film director) whom Claude Chabrol especially disliked, and also made fun of in his earlier film "Les Biches".