Poirot’s gaze took on an admiring quality. “You have been of a marvellous promptness,” he observed. “How exactly did you go to work, if I may ask?”

“Certainly,” said the inspector. “To begin with⁠—method. That’s what I always say⁠—method!”

“Ah!” cried the other. “That, too, is my watchword. Method, order, and the little grey cells.”

“The cells?” said the inspector, staring.

“The little grey cells of the brain,” explained the Belgian.

“Oh, of course; well, we all use them, I suppose.”

“In a greater or lesser degree,” murmured Poirot. “And there are, too, differences in quality. Then there is the psychology of a crime. One must study that.”

“Ah!” said the inspector, “you’ve been bitten with all this psychoanalysis stuff? Now, I’m a plain man⁠—”