Curious things, habits. People themselves never knew they had them. [Witness for the Prosecution, also published in The Hound of Death and Other Stories.]

... obsessions are always dangerous.

Time does not dispose of a question - it only presents it anew in a different guise.

a lot of trouble has been caused by memoirs. Indiscreet revelations, that sort of thing. People who have been close as an oyster all their lives seem positively to relish causing trouble when they themselves shall be comfortably dead.

Everybody is very much alike, really. But fortunately, perhaps, they don't realise it. - Miss Marple

Men don't understand how their mannerisms can get on women's nerves so that you feel you just have to snap.

It's so much nicer to be a secret and delightful sin to anybody than to be a feather in his cap.