Hermione didn't understand her need to be snarky in response to his statement. It just sort of happened. At least Rodolphus was in a pleasant enough mood that he didn't feel the urge to launch himself across the room at her throat again. Ginny must've put in extra effort to make him satisfied the night before. She didn't really want to think about their sex life, but at least with Ginny keeping him entertained in the bedroom, her own services were less likely to be needed.