“You should employ your little grey cells”

“It is the brain, the little gray cells on which one must rely. One must seek the truth within--not without." ~ Poirot”

“Excuse me, Monsieur Poirot. If you'd like to ask any questions, I'm sure the doctor wouldn't mind.Of course not. Of course not. Great admirer of yours, Monsieur Poirot. Little gray cells -- order and method. I know all about it.”

“Katherine Grey was born with the power of managing old ladies, dogs, and small boys, and she did it without any apparent sense of strain.”

“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!”

“How little you might know of a person after living in the same house with them!”

“You're a man milliner, Poirot. I never notice what people have on.""You should join a nudist colony”