Justification of the Ugly Jumper

It wasn't that she wished he was dead, Petunia reflected as she clutched the jumper in her hands: She just wished she didn't know he was alive. What is the story behind that one paragraph, describing the one time Harry got away with magic as a child? Snape wasn't the only one controlled by Lily's eyes…A character portrait revealing Petunia Evan's Dursley's one moment of humanity.