Harry Potter: [about the Thestrals] So why can't the others see them?
Luna Lovegood: The only people who can see them are those who've seen death.
Harry Potter: So, you've known someone who died?
Luna Lovegood: My mum. She was quite an extraordinary witch, but she did like to experiment, and one day, one of her spells went badly wrong. I was nine.
Harry Potter: I'm sorry.
Luna Lovegood: Yes, it was rather horrible. I still feel very sad about it sometimes. But I've still got Dad.