[From Wikipedia:] “Hans was a horse owned by Wilhelm von Osten, who was a mathematics teacher, an amateur horse trainer, phrenologist, and something of a mystic. 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. Von Osten would ask Hans,”If the eighth day of the month comes on a Tuesday, what is the date of the following Friday?” Hans would answer by tapping his hoof. Questions could be asked both orally, and in written form. Von Osten exhibited Hans throughout Germany, and never charged admission.”
Clever Hans was able to do math, write and read German, and many other tasks. But Clever Hans is perhaps one of the best examples of what happens when one doesn’t account for demand characteristics: he was reading the audience and the experimenter, and not solving any problems independently.
