"Yes. They are set differently. The two eyes, I mean. They look as if they belonged to different faces."
"I thought you hadn't met many."
"No, but I've read all the case histories and studied the photographs. I've always been surprised that no book on murder mentions it, it happens so often. The inequality of setting, I mean."
"So it's entirely your own theory."
"The result of my own observation, yes. You ought to have a go at it sometime. Fascinating. I've got to the stage where I look for it now."
"In the street, you mean?"
"No, not quite as bad as that. But in each new murder case. I wait for the photograph, and when it comes I think: 'There! What did I tell you! "
"And when the photograph comes and the eyes are of a mathematical identity?"
"Then it is nearly always what one might call an accidental murder. The kind of murder that might happen to anyone given the circumstances."
"And when you turn up a photograph of the revered vicar of Nether Dumbleton who is being given a presentation by his grateful parishioners to mark his fiftieth year of devoted service, and you note that the setting of his eyes is wildly unequal, what conclusion do you come to?"