The additional scene at the end, in which Ewan McGregor and Renée Zellweger perform a duet, was filmed at the behest of Zellweger and McGregor. They pointed out that, since both had previously appeared in musicals (McGregor in Moulin Rouge! (2001) and Zellweger in Chicago (2002)), it would have been a sin not to include one.
Barbara Novak's extended monologue, performed by Renée Zellweger, runs for three minutes and two seconds in a single, uninterrupted take and was completed successfully in just six takes.
Vikki Hiller (Sarah Paulson) suspects Peter MacMannus (David Hyde Pierce) of being gay. Although he isn't presented that way in the film, within just a few years both Pierce and Paulson publicly came out as homosexual.
Every single item the characters wore — quite literally from head to toe — was made-to-measure for them.
The split-screen telephone-call sequences are explicit tributes to screwball comedies of the 1950s and 1960s, most notably Pillow Talk (1959).
To achieve the film's vivid, stylised look, cinematographer Jeff Cronenweth digitally colour-timed the film to replicate the appearance of three-strip Technicolor.
In a curious coincidence, Judy Garland appeared on a black-and-white TV programme performing 'Down With Love'. Renée Zellweger subsequently won an Academy Award for her portrayal of Garland in Judy (2019).
Tony Randall (Theodore Banner) co-starred alongside Rock Hudson and Doris Day in Pillow Talk (1959), Lover Come Back (1961) and Send Me No Flowers (1964). Across all three films Randall portrayed Hudson's employer and his nebbish sidekick — the part that David Hyde Pierce plays in this film.
In the dating montage one of the background shots shows a man playing the bongo drums. That clip was taken from the sequence in Pillow Talk (1959), in which the characters portrayed by Doris Day and Rock Hudson first meet.
Renée Zellweger and Ewan McGregor sang the duet during the film's finale.
A number of lines of dialogue refer to "Nazi rocket engineers". This alludes to Operation Paperclip, the post‑Second World War US government initiative that relocated the Nazi scientists who developed the V-2 rockets that bombed London to the United States to work on the early US space programme, largely centred in Huntsville, Alabama. The best‑known of these men, Wernher von Braun, had been the technical director of a Nazi rocket facility that relied on slave labour from the nearby Mittelbau‑Dora concentration camp. Von Braun was instrumental in developing the Redstone missile, which formed the basis of the US missile programme, and the Saturn V rocket, which underpinned the Apollo programme that sent American astronauts to the Moon.
Cartoon animator and MAD Magazine artist Richard Williams created a counterfeit MAD Magazine cover depicting 'Alfred E. Neuman' as Barbara clutching her book. MAD Magazine observed that the publication's cameo in the film was a guaranteed kiss of death for the picture.
Renée Zellweger's costumes were designed by the Montreal-based clothing firm Le Chateau.
Renée Zellweger and Ewan McGregor also co-starred in Miss Potter (2006), where once more they portrayed one another's romantic interests.
Director Peyton Reed has pointed to the popular auction site eBay as a handy place to find period costumes and props for the film.
A total of fifty-five sets were constructed across four sound stages.
This was the final cinema release to include Florence Stanley, cast as the Dry Cleaner's Wife.
On 4 August 2003, Ewan McGregor was present at the Australian gala premiere of the film, as he was in the country to shoot Star Wars: Episode III - Revenge of the Sith (2005). George Lucas was also in attendance.
The MAD Magazine front cover was a forgery, whereas the rear cover came from a genuine issue dating from the late 1960s.
The mean shot length is roughly 5 seconds. The median shot length is approximately 4.5 seconds.
Rachel Dratch and Chris Parnell made brief appearances in this film (Dratch as Gladys, one of Barbara Novak's friends and co-workers, and Parnell as a television presenter). At the time, they were also members of the cast of Saturday Night Live (1975).
This marked director Peyton Reed's first time working with the Panavision anamorphic format. He later returned to the format when he directed two episodes in series two of The Mandalorian (2019) (Chapter 10: The Passenger (2020) and Chapter 16: The Rescue (2020)).
This is the sole film in Peyton Reed's directorial filmography that failed to claim the No. 1 spot on its opening weekend.
Judy Greer was under consideration to portray Barbara Novak.
Elizabeth Mitchell was considered for the role of Barbara Novak.
Tia Carrere was under consideration to portray Barbara Novak.
David Hyde Pierce's character is called Peter McMannus; this is the same name attributed to the production accountant in the film's end‑credits (Peter McManus).
