According to Mia Farrow, the scenes where Rosemary walks in front of traffic were spontaneous and genuine. Roman Polanski is reported to have told her that "nobody will hit a pregnant woman." The scene was successfully shot with Farrow walking into real traffic and Polanski following, operating the hand-held camera since he was the only one willing to do it.
Before the filming of the scene of Rosemary calling Donald Baumgart (the actor in the story who mysteriously goes blind), Mia Farrow did not know who would be speaking the lines. It was that of Tony Curtis, and in the scene, Farrow shows slight confusion, unable to place the voice. This confusion was exactly the effect director Roman Polanski hoped to capture by having Curtis read the lines.
Ira Levin felt that this film is "the single most faithful adaptation of a novel ever to come out of Hollywood." William Castle speculated the reasons for this were because it was the first time Roman Polanski had ever adapted another writer's work, unaware he had the freedom to improvise on the book.