Murder on the Orient Express
"I look first at my witness, I sum up his or her character, and I frame my questions accordingly. Just a little minute ago I am asking questions of a gentleman who wants to tell me all his ideas on every subject. Well, him I keep strictly to the point. I want him to answer yes or no, this or that. And then you come. I see at once that you will be orderly and methodical. You will confine yourself to the matter in hand. Your answers will be brief and to the point. And because, Mademoiselle, human nature is perverse, I ask of you quite different questions. I ask what you feel, what you thought. It does not please you this method?" (2.11.32)
"Are these people whose evidence we have taken speaking the truth or lying? We have no means of finding out – except such means as we can devise ourselves. It is an exercise, this, of the brain." (3.1.12)
"Lies – and again lies. It amazes me, the amount of lies we had told to us this morning."
"There are more still to discover," said Poirot cheerfully.
"You think so?"
"I shall be very disappointed if it is not so." (3.5.58-61)