If a man is told that he is at the North Pole and he believe what he is told, he’ll show physical signs which suggest that his body is reacting as though he were at the North Pole. He’ll go pale and shiver. If a hay fever sufferer is shown a photograph of the sort of plant to which he is allergic, he’ll sneeze. When the film Lawrence of Arabia was shown, cinema managers around the world reported that the sales of the ice cream rocketed. The endless desert scenes had made the patrons fell uncomfortably hot.