The grandfather was surprised that she would ask such a question, but decided that if she's old enough to know to ask the question, then she's old enough to get a straight answer. Composing himself to leave nothing out, he proceeded to tell her all about human reproduction and the joys and responsibilities of intercourse.
When he finished explaining, the little girl was looking at him with her mouth hanging open, eyes wide in amazement.
Seeing the look on her face, the grandfather asked her, "Why did you ask this question, honey?"
The little girl replied, "Grandma says that dinner will be ready in just a couple of secs."