"Belle de jour" is a day lily in French, a flower that blooms only by day, as Severine is available only during the afternoons. "Belle de jour" is also a sort of pun, as it reminds us of "belle de nuit", an euphemism for prostitute.
Catherine Deneuve's famous buckled shoes were designed by Roger Vivier.
According to Luis Buñuel scholar Julie Jones, Buñuel once said that he himself didn't know what the end exactly means.
In most subtitled versions of the film, an italicized font is used to help the audience spot Séverine's fantasies from reality.
In the rape scene, her dress was fitted with Velcro to give off a tearing sound as it was ripped away.
The comment by Pierre Serizy, "Semen retentum venenum est" is in Latin, and could be roughly translated as "To retain one's semen is poisonous" or "To retain one's semen will allow it to eat away at one like a poison."
Luis Buñuel:
Sitting in the outdoor café when the Duke gets off his carriage.