One of the first scenes to be filmed called for Ingrid Bergman and Anthony Perkins to share a passionate kiss. Bergman had found a similar situation while she was filming Luz que agoniza (1944) extremely uncomfortable. In that film, she was forced to shoot an intimate and romantic scene with Charles Boyer on the first day of production, minutes after meeting the man. Bergman so disliked the experience of kissing a man she had just met on screen that she vowed never to do it again. When she was once again asked to film a romantic scene with a man she hardly knew for this film, Bergman took action. She asked Perkins to practice kissing her privately, in her dressing room, before their scene was filmed on camera. According to Bergman, Perkins obliged, and by the time they performed their scene in front of the camera neither actor found the scene uncomfortable.
Phillip's line, "All's for the best in this best of all possible worlds", is from "Candide" by Voltaire.
The uncredited appearance by Yul Brynner was due to the fact that he was on a photographic assignment. He had worked with director Anatole Litvak the previous year on The Journey (1959), and the subject of his camera was Ingrid Bergman.
Ingrid Bergman, Anthony Perkins and Jean-Pierre Cassel appeared together in Muerte en el expreso de Oriente (1974).