Final answer:
Psychologist Oskar Pfungst discovered that Clever Hans, a horse thought to be able to carry out intellectual tasks, was actually responding to unintentional cues from his handler.
Step-by-step explanation:
The question refers to the case of Clever Hans, a horse that was believed to be able to perform arithmetic and other intellectual tasks. The determination of unintentional signaling to Hans was made by Oskar Pfungst, a psychologist. Pfungst conducted experiments that ruled out any form of intentional communication between the horse and its handler. He showed that the horse was responding to subtle cues like body language and changes in the handler's facial expression, which were given unintentionally when the horse made the correct movements towards the answer.