Clever Hans

In 1904, a Berlin horse called Clever Hans seemed to solve sums and answer questions by tapping its hoof, and a commission could find no trick.

1904 CE · 52.54, 13.40 · status: explained

The sceptical view

In 1907 psychologist Oskar Pfungst showed the horse read tiny unconscious cues from its questioners: the 'Clever Hans effect'.

Sources

1. Wikipedia: Clever Hans