Wrinkling her nose as the mention of flexible indoor plumbing, she still listened in on his little ramble. However when he mentioned his grandparents did not know what Slytherin was, her eyebrow raised slightly. Her mind quickly set up how to proceed. He was obviously of muggle heritage, which meant that it was unlikely that he would have ties to more forceful members of the pureblood community. While she could take a proper purist stance, she felt that was unwise and frankly she really did not want to. So she settled mentally on simply keeping a vague line of conversation on that topic, which would make denying anything he decided to repeat easier.
"Many people like me, grandparents included." she said innocently enough. It was best to just not talk on that topic. There was enough violence going on already.
Smiling slightly, she looked over to the door. "You know." she pondered aloud, chewing her lip a bit thoughtfully. "I think it'd depend on the prefect." Looking back at him, she laughed slightly. "Yeah, no I don't think they'd expect anything like that going on."