Clever Hans

n. The name of a horse famous in the early 1900s for being able to give the correct answer to any question its owner asked of it by tapping its hooves on the ground. It was eventually found that Clever Hans could only answer questions to which his owner knew the answer and only when he could see his owner, and it was supposed that the owner was unconsciously giving Hans cues and rewards when he tapped his feet appropriately to answer questions. This story has been used ever since that time as an example of reaching false conclusions by overlooking important variables in research.