The younger sister was so hot she was moaning loudly that even the older sister got aroused and rushed into the bathroom. (NHDTB-228)

Knowing his girlfriend's older sister was sexually frustrated, the man deliberately had sex with his girlfriend in a way that the sister, who was in the next room, could hear. The sister, aroused, also listened and masturbated. After they finished and he went to shower, the sister rushed in after him!