After getting into her make up for the first time, Gwyneth Paltrow spent the rest of the day walking around in public. No one recognized her, and she used people's reaction to her as an obese woman to help understand her character in the film.
When Rosemary jumps in the pool, the huge splash was created by two wide hoses (which Gwyneth Paltrow had to dive between) which shot off the streams of water on either side of her, simulating a huge splash of water.
According to the DVD commentary, the Farrelly brothers stated that the line, "Well I can squeeze them and that's real enough for me" was changed to avoid a R rating by the MPAA. The original quote from the script was, "Well I could suck on them and that's real enough for me".
In Roger Ebert's review he states, "Only the most attentive audience members will catch the Farrellys' subtle reference to a famous poem by Emily Dickinson." Ebert's reference is to a fly that buzzes in the death scene of Hal's father; the poem is, "I heard a Fly buzz - when I died"