Dead Ringers is a 1988 Canadian-American psychological thriller film starring Jeremy Irons in a dual role as identical twin gynecologists. David Cronenberg directed and co-wrote the screenplay with Norman Snider; their script was based on the novel Twins by Bari Wood and Jack Geasland. The film is very loosely based on the lives of Stewart and Cyril Marcus. Wikipedia
Beverly, Age 9: Are you thinking what I'm thinking?
Elliot, Age 9: Yeah. You ask her.
Beverly, Age 9: Raffaella, will you have sex with us in our bathtub? It's an experiment.
Raffaella: Are you kidding? Fuck off, you freaks! I'm telling my father you talk dirty. Besides, I know for a fact you don't even know what "fuck" is!
(she walks off)
Beverly, Age 9: They're so different from us...