Emily Blunt was at the beginning stage of pregnancy at the start of filming. She kept this a secret from the cast and crew except for her friend, co-star Justin Theroux. Director Tate Taylor only found out of the case towards the end of filming when filming a scene of Rachel showering, he noticed that her bump was bigger then it was before and went to confront her whether if she had withheld information that was privy to him. Blunt eventually had to reveal it to Taylor and he also agreed to keep it secret. By the time filming ended in February 2016, she was in her fifth month of pregnancy.
The book that this film is based on is actually set in England, and Rachel Watson gets the train into London. Emily Blunt is from London, England. For this film, the location was changed to New York but Rachel speaks with Emily's natural British accent in keeping with author Paula Hawkins' vision.
The novel debuted at No. 1 on The New York Times Fiction Best Sellers of 2015 list and remained in the top position for fifteen weeks, thirteen of which were consecutive. The book had sold more than 3 million copies in the United States alone as of July 2015.
Friends (1994) reference: When Lisa Kudrow's character sees Rachel (Emily Blunt) on the train, she excitedly exclaims, "Rachel! I haven't seen you in a million years!" Kudrow's character on the sitcom, Phoebe Buffey, was best friends with Rachel Green (Jennifer Aniston). Coincidentally, Aniston's real-life husband, Justin Theroux, plays Rachel's ex-husband in this film.
On September 21, 2015, this was reported that Jared Leto and Chris Evans were in talks to join this film, where Evans would play Tom Watson, Rachel's ex-husband, and Leto would play the neighbor's husband.
The trivia items below may give away important plot points.
In this film, Rachel Watson is infertile. Coincidently, Emily Blunt was pregnant during filming. This Coincidence also occurred during filming of Into the Woods (2014) in which Blunt plays a character who can not get pregnant. However, she was in real life.
Darren Goldstein, otherwise known as the Man in the Suit in this film, is a featured actor on Showtime's The Affair. Incidentally, the hit cable show also features a storyline heavily based on interwoven extramarital affairs and murder.