3 sisters

3 sisters return home from college with their new boyfriends in tow. One night their mother fancies a glass of water before bed. On her way back she stops in front of the door of each girls room being nosy. At the first door she hears uncontrollable laughter coming from her daughter. She moves to the second door and hears her second daughter yelling and groaning. She moves on to the third door and is surprised to hear nothing.The next morning at breakfast she decides to ask her daughters about the noises. She ask the first why she was laughing. The daughter replies I've always been taught if it tickles to laugh. She ask the second daughter about the yelling and groaning. Her daughter says Ive always been taught if it hurts to yell. She moves on to her last daughter and says how its strange that she didn't hear anything coming from her room. Her daughter replies, "Mom you taught to never speak with my mouth full".