The Mitchell-Hedges Skull

The most famous of the crystal skulls: by the family's account Anna Mitchell-Hedges found it in 1924 in the ruins of the Maya city of Lubaantun in British Honduras, on her seventeenth birthday. It was called an instrument of ancient priests and an object that stops the heart. The documents say otherwise: Anna's adoptive father Frederick Mitchell-Hedges bought it at Sotheby's in London in 1943 from the collector Sydney Burney, and it appears in Burney's correspondence before that. In 2008 Jane Walsh and the Smithsonian's laboratory examined it under an electron microscope: the surface was worked with a rotary abrasive tool, which pre-Columbian America did not have.

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Clever Hans

The residential inner courtyard at 10 Griebenowstraße in the Mitte district of Berlin, Germany. At the turn of the 20th century, this urban setting hosted public demonstrations of the Orlov Trotter stallion known as Clever Hans (Der Kluge Hans). The horse's apparent mastery of arithmetic and human language captivated international audiences, revolutionized animal cognition research, and led to the discovery of the observer-expectancy effect ("Clever Hans effect").