A teenage girl come home from school and asks her mother, "Is it true what Rita just told me?"

"What's that?" asks her mother. "That babies come out of the same place where boys put their penises?" said her daughter.

"Yes it is dear!" replies her mother, pleased that the subject had finally come up and that she wouldn't have to explain it to her daughter.

"But then, when I have a baby," responded the teenager, "won't it knock my teeth out?"