SUGGESTED ANSWER TO QUESTION 2A-3(c)

A series of experiments showed that the effects of an important extraneous variable had not been controlled for: the body, head, and facial movements of the people who were presenting Hans the arithmetic problem (see Wozniak, 1999, for a brief summary of the experiments performed by Oskar Pfungst and published by him in 1907). Regardless of what problem he was given to solve, Hans would start tapping his hoof and would not stop until the person asking the question made small movements of his body, head, or face--movements which the person was not aware of. The human questioner typically made these movements as Hans reached the correct solution to the problem, at which time Hans would get his reward. Thus, Hans was not adding the numbers in his head at all. He simply was extremely sensitive and responsive to the body, head, and facial movements of humans.