Every reaction to a stimulus, however slight, was completely indicative of all the trifling changes, of all the flickering currents that went on in another's mind. The First Speaker could not sense the emotional content of the Student's instinctively, as the Mule would have been able to do - since the Mule was a mutant with powers not ever likely to become completely comprehensible to any ordinary man, even a Second Foundationer - rather he deduced them, as the result of intensive training.