Poirot said placidly, One does not, you know, employ merely the muscles. I do not need to bend and measure the footprints and pick up the cigarette ends and examine the bent blades of grass. It is enough for me to sit back in my chair and think. It is this – he tapped his egg-shaped head – this, that functions!
Murder Preferred: Including: The Patriotic Murders; A Murder is Announced; Murder in Retrospect (ed. 1960)