“He recognized a portrait of Einstein because he picked up the characteristic hair and moustache; and the same thing happened with one or two other people. ‘Ach, Paul!’ he said, when shown a portrait of his brother. ‘That square jaw, those big teeth— I would know Paul anywhere!’ But was it Paul he recognized, or one or two of his features, on the basis of which he could make a reasonable guess as to the subject’s identity?”