Clever Hans the Math Horse
Clever Hans Effect is a term used for the effect of subtle body language by a questioner on their subjects. It’s named after a 19th century horse who was trained in math — tapping six times when the answer is six, and so on. Investigations revealed that it was no fraud: Hans was simply reading the subtle body language of the questioner, who would unconsciously (and without the ability to suppress it, even when made aware of the fact) emit special signs when the correct number of taps was reached.
This technique should come in handy if you’re ever on a game show where you get alternatives for the answer: just waver about a bit and watch the questioner’s signs. And, of course, it’s similar to what exposes amateur poker players. Most humans aren’t quite so skilled in reading body language, however, so I’d say this horse was very clever indeed.
