Harry, do you know why it is that Professor Quirrell could not ...
Dumbledore: Harry, do you know why it is that Professor Quirrell could not bear to have you touch him?
[Harry shakes his head]
Dumbledore: It was because of your mother. She sacrificed herself for you, and that kind of act leaves a mark.
[Harry reaches up to touch his scar]
Dumbledore: No no, this kind of mark cannot be seen. It lives in your very skin.
Harry: And what is that?
Dumbledore: Love, Harry. Love.