"3 Weddings" joke

Three sisters decided to get married on the same day to save their parents the expense of separate weddings. As a further step to reduce the price tag, the three sisters resolved to spend their honeymoon night at home.
Later that night, their mother couldn't sleep, so she went to the kitchen for a cup of tea.
On her way, she tiptoed by her oldest daughter's bedroom and heard her screaming.
The mother thought to herself, "That's normal, especially on her wedding night."
She snuck by her second oldest daughter's room and heard her laughing.
"That's normal too," she said, smiling to herself.
Finally, she slipped by her youngest daughter's room where she didn't hear a peep, but she thought nothing of it.
The next morning in the kitchen, after the husbands had gone out, the woman asked her eldest daughter about last night's noises. "Well Mom," she replied, "you always said if it hurt I should scream."
"You're absolutely right sweetheart," the mother assured her, turning to her middle daughter. "Now why were you laughing?" she asked.
"You always said if it tickled, I could laugh," she answered.
"True enough, honey." The mother smiled, remembering her newlywed days. "Now it's your turn, baby," she said turning to her youngest daughter. "Why was it so quiet in your room last night?"
"Mom, don't you remember? You always told me never to talk with my mouth full."