In early 1900s Berlin, a math teacher asked his horse to divide fractions, and the horse tapped out the correct answer. Skeptics assumed a trick, a hidden wire, a trained signal. The real discovery was far stranger: the horse had accidentally exposed a subconscious flaw in human psychology that still haunts science today.

This episode tells the story of Clever Hans, the horse who fooled a scientific commission into declaring he could do math. We follow the rigorous investigation that cracked the case and trace how the Clever Hans effect reshaped experimental method and still trips up modern animal research and artificial intelligence.

• The cultural moment after Darwin that made Germany hungry to believe animals were smarter than assumed
• The 13-member Hans Commission, including a circus manager, zoo director, and cavalry of ...