Pfungst carried out laboratory tests with human subjects, in which he played the part of the horse. Pfungst asked subjects to stand on his right and think "with a high degree of concentration" about a particular number, or a simple mathematical problem. Pfungst would then tap out the answer with his right hand. He frequently observed "a sudden slight upward jerk of the head" when reaching the final tap, and noted that this corresponded to the subject resuming the position they had adopted before thinking of the question.