Harry Potter and the Half-Blood Prince2009

Horace Slughorn:
[Telling Harry the story of his deceased fish] It was a student who gave me Francis. One spring afternoon I discovered a bowl on my desk with just a few inches of clear water in it. And floating on the surface was a flower petal. As I watched, it sank. Just before it reached the bottom, it was transformed into a wee fish. It was beautiful magic, wonderous to behold. The flower petal had come from a lily. Your mother. The day I came downstairs, the day the bowl was empty, was the day your mother... I know why you're here, but I can't help you. It would ruined me.