The graveyard spin occurs when the semicircular canals (in the ear) reach equilibrium during a sustained turn. Because the semi-circular canals detect motion (see http://thalamus.wustl.edu/course/audvest.html for more information), equilibrium in this system can result in effects on the pilot’s perception of events. The pilot can lose the perception that the turn is still occurring, and can decelerate upon spin recovery. If the pilot decelerates on spin recovery, he or she would have the sensation of a spin in the opposite direction, even if no spin was occurring. A pilot respond inappropriately by applying back pressure to the controls and adding power, which would result in re-entering the spin in the original direction, possibly in a tigher spin, and in loss of control of the aircraft.