A man, blindfolded and spun slowly in a rotating chair, will think when the chair slows that it has stopped. When it has stopped, he will think it has begun to spin the other way. The mistake happens deep in his ear, among the tiny hair cells and drifting fluid inside the semicircular canals of the bony labyrinth. These are the minute, impossibly fragile internal instruments that detect the yaw, pitch, and roll of the human head—wondrous little gizmos to be sure but poorly evolved for flight.
