Look for something hard enough and it's possible to find evidence of it, even if it's not actually there, says Stuart Blackman. Take the story of the horse Clever Hans for example...
Who was Clever Hans?
Take the case of Clever Hans, the German horse who enthralled crowds at the turn of the 20th century with his apparent ability to count, spell, perform complex arithmetic, distinguish musical intervals and remember people's names, giving the answer by stamping a hoof the right number of times.
- Surely animals need a brain to be clever? Not always... Discover some remarkably clever, yet brainless animals
- The smartest animals in the world: Discover the cleverest creatures in the animal kingdom - and there may be some surprises
"He can do almost everything but talk," gushed The New York Times. Eminent scientists of the day also hailed his genius, and it took a rigorous, unsentimental study led by a bright young psychologist called Oskar Pfungst to demonstrate what was actually going on.
How clever was he really?
In 1907, Pfungst established that Hans only ever answered questions correctly when the questioner also knew the answer. Rather than performing the mental gymnastics himself, Hans was merely responding to subtle - and unconscious - changes in the questioner's posture and facial expression that gave him the cue to start and stop stamping.
What Hans was really revealing was the human capacity for self-deception. The Clever Hans Effect revolutionised the way we study animals and people.
Had this handsome equine - a member of the Orlov Trotter breed - been able to do everything it was claimed he could, the world would be a very different place. As it is, we have him to thank for plugging some gaping holes in the scientific method.
Main image: maths teacher Wilhelm von Osten and his horse named Clever Hans, which purportedly was able to read and compute.