Deborah Kerr and Cary Grant improvised many of their scenes throughout filming, and a number of lines that made it to the final cut of the film came from the actors' improvisation.
The 53-year-old Cary Grant was only 15 years younger than Cathleen Nesbitt, who played his grandmother. Even at Janou's stated 82 years, she would only be 29 years older than her "grandson's" real age.
The film was shot mostly in Hollywood, though there were location shoots in New York City and the South of France. When Cathleen Nesbitt's friends asked if she had enjoyed filming her scene as Cary Grant's grandmother in France, she had to inform them that the interior scenes had been done on the 20th-Century-Fox back lot.
During production, Cary Grant's wife, Betsy Drake, had him visiting a hypnotist to help him quit smoking. She also packed him a hamper full of health food for his lunch, though he often finished it before starting filming because without cigarettes he was hungry all the time.
Cary Grant, who had started smoking in 1911, gave up his 60-a-day cigarette habit during filming, although he continued to smoke an occasional cigarette for several more years.