Clever Hans and his effects: Karl Krall and the origins of experimental parapsychology in Germany.

Shortly before the outbreak of World War I, the so-called Elberfeld horses, the counting and speaking animals, were among the most debated subjects of the newborn comparative psychology. Yet, they have left little trace in the historiography of this discipline, mostly as an appendix of the more famous Clever Hans. Their story is generally told as the prelude to the triumph of reductionistic experimental psychology. By paying a more scrupulous attention than has so far being done to the second life of Hans, and to the endeavours of his second master, Karl Krall, this article explores the story of the Elberfeld horses as an important, if so far neglected, chapter in the history of experimental parapsychology.