A horse tricked people into thinking he could do math.

In the early 20th century a horse named Clever Hans was trained by his owner Wilhelm von Osten, to answer simple question. Hans was said to have been taught to add, subtract, multiply, divide, work with fractions, tell time, keep track of the calendar, differentiate musical tones, and read, spell, and understand German. Questions could be asked verbally or written down, and Hans would answer by tapping his hoof. He was wrong occasionally, but was generally about 89% accurate. However after a formal investigation in 1907, psychologist Oskar Pfungst demonstrated that the horse was not actually performing these mental tasks, but was watching the reaction of his human observers. Hans could read the subtle body language of the questioner (who knew the answer to the question) and would stop tapping his hoof when the involuntary change in body language signalled the correct answer.
http://en.wikipedia.org/wiki/Clever_hans