The performing horse Clever Hans with his trainer, Wilhelm von Osten, 1904. Source: Britannica
The Clever Hans effect refers to a psychological phenomenon where an animal (or human) appears to solve complex cognitive tasks, but is actually responding to unconscious, non-verbal cues given off by the person asking the question.

It demonstrates how easily human observers can accidentally influence an outcome without realizing it.

Reference

Crawford, K. (2021). Atlas of AI: Power, politics, and the planetary costs of artificial intelligence. Yale University Press