Oliver had already mentioned once before about the Gryffindor ghost who liked to prank Professor McGonagall with Peeves the Poltergeist. Though she didn't want to even think about the possibilities, she knew who he was talking about. She felt her eyes burn with tears she didn't want to shed in front of her son. It was too hard to think about Fred Weasley being dead. Even after twenty years she found it easier to just not think about him at all than to imagine him as one of the spirits haunting Hogwarts. When she allowed herself to remember that it was Augustus who was the one who cast the spell that ended his life... it was best that she try to forget him entirely.