Agatha Christie said this quote

Such nice people, the Hillingdons, though she's not really very easy to know, is she? I mean, she's always very pleasant and all that, but one never seems to get to know her better.'Miss Marple agreed thoughtfully. 'One never knows what she is thinking.''Perhaps that is just as well.''I beg your pardon?''Oh nothing really, only that I've always had the feeling that perhaps her thoughts might be rather disconcerting.