An episode from the life of William James captures the problem well. He had been given charge of a turtle's heart for a popular lecture on physiology by one of his Harvard Medical School professors. The lecturer was demonstrating that the heart would pulsate when certain of its nerves were stimulated, and the pulsations were projected onto a screen at Sanders Theatre. Halfway through the lecture, James realized the heart was not responding, so he took it upon himslef, in a sudden and almost automatic response to the emergency, to make the proper motions on the screen by manipulating his forefinger such that the audience would not fail to gain a true understanding of the heart's physiology. Writing many year later-in a final essay on psychical research that was centrally about the balance of fraud and faith in what we can know-James admits that such simulation could be disdained as shameless cheating. Had he acted otherwise, however, the audience would have been cheated of an understanding of physiology. His forefinger had performed humbug in the service of understanding.
--from John Durham, Speaking into the Air