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

Sometimes I feel sure he is as mad as a hatter and then, just as he is at his maddest, I find there is a method in his madness.

You cannot mix up sentiment and reason.

At the small table, sitting very upright, was one of the ugliest old ladies he had ever seen. It was an ugliness of distinction - it fascinated rather than repelled.

He was very much a man of moods, possibly owing to what is styled the artistic temperment. I have never seen, myself, why the possession of artistic ability should be supposed to excuse a man from a decent exercise of self-control.

Imagination is a good servant, and a bad master.

I know there's a proverb which that says 'To err is human,' but a human error is nothing to what a computer can do if it tries.