Clever Hans answered arithmetic by reading human faces. 🐴

Clever Hans answered arithmetic by reading human faces. 🐴 . . . Beginning in 1904, the Berlin horse tapped his hoof to answer sums before astonished crowds. In 1907, psychologist Oskar Pfungst ran controlled tests and found Hans succeeded only when someone present knew the answer. He could not calculate—but he repeatedly detected movements his questioners did not know they made.