'Becky Raped by the Horse Trainer'
After disclosing that their father beat them with a belt, Margot and Pauline say that their unseen sister, Becky, had it the worst because she was "raped by the horse trainer." Margot and Pauline then explode into hysterical laughter.
So...were they joking (and putting everyone else on in the room, especially Malcolm) when they said it? Or are they alluding to perhaps Becky having a consensual sexual relationship with the horse trainer, which their father disapproved and perhaps said it was rape?
If Becky was raped, it's not something that one should laugh at.
Any ideas?