Rachel Weisz would shoot an entire scene as Elliot first, acting opposite her scene partner and stand-in, Kitty Hawthorne, before heading back into hair and makeup to transform into Beverly. Then she'd act out the same scene with an earpiece in place so she could hear her own lines.
The names of the twin main characters, Beverly and Elliot, are unchanged from the 1988 movie in which the twins were male.
Two characters have the surnames of Cotard and Capgras, the namesake of two delusions. The Cotard delusion involves the sufferer believing they are dead or have lost vital parts in some way. Fitting for the subject matter, Capgras delusion has the sufferer believing loved ones have been replaced by a perfect physical duplicate.
The TV show Genevieve stars in is called "Rabid", the same name as David Cronenberg's 1977 film.