"If you say so," he says dubiously, meaning the understanding, which in his opinion conflicts with the nervousness. "It is, but she wasn't one when you were there. The Headmaster took her on in '95, after the house she served became extinct. That's rather the problem; she hasn't adjusted well to serving the castle rather than a small home."
"Why do you think?" he counters, putting it back on him. "We have a spell with the effect of a charm rather than a hex, responsive to a nonmagical action, which responds to magical investigation and deconstruction attempts with bizarre but harmless defensive actions. Speculate."