The cerebellum, Latin for little brain, sits at the back of the skull beneath the cerebral hemispheres and is found in all vertebrates. In humans it does not start movements, but fine-tunes them, taking in signals from the spinal cord and other brain areas to coordinate balance, posture and precise timing. Its surface is covered in fine parallel grooves because its cortex is a thin sheet folded like an accordion, packed with Purkinje and granule cells. Damage to it causes unsteady, clumsy movement, while its role in learning movements, such as riding a bike, is well established. It also contributes to attention, language and emotional responses, though these functions are less firmly understood.

In 1909 D. W. Griffith made a 14-minute film about a speculator who corners the wheat market and doubles the price of bread. A farmer sows his field while a 'Wheat King' gambles in the Chicago wheat pit; bakers raise the loaf from five cents to ten and the poor line up for bread. Griffith cut back and forth between the farm, the feast and the breadline, a technique called parallel editing, so audiences saw both ends of the economy at once. The film drew on Frank Norris's stories and on a real scheme: months earlier Chicago financier James Patten had cornered wheat, sent bread prices up and made about $5 million, roughly $185 million today.