"Neville," Harry told Ron sagely. He looked around again and then shrugged. "Maybe she wanted to go back early? To be with everyone else? And didn't want to come back to a messy room?"
Still, with Ron going on about it, Harry felt a little odd about it too. "Maybe we should go find Xenophilius - see if he needs help, and if there's anything else he has to say, and then get out of here? Just in case?" Paranoid, probably - but at this point better paranoid and alive than the alternative.