<Li> Using questioners other than the horse's master </Li> <Li> By means of blinders, varying whether the horse could see the questioner </Li> <Li> Varying whether the questioner knew the answer to the question in advance . </Li> <P> Using a substantial number of trials, Pfungst found that the horse could get the correct answer even if von Osten himself did not ask the questions, ruling out the possibility of fraud . However, the horse got the right answer only when the questioner knew what the answer was and the horse could see the questioner . He observed that when von Osten knew the answers to the questions, Hans got 89 percent of the answers correct, but when von Osten did not know the answers to the questions, Hans answered only six percent of the questions correctly . </P>

Clever hans could answer math questions only under which conditions ​