“Crank” is slang for a low purity, crystallized Methamphetamine
that is administered in a powder form. Crank, like all other Methamphetamines, is a stimulant that acts on the central nervous system to increase heart rate and alertness of its users. Highs on the drug last between 8 and 24 hours, and often include a violent "crash" period where the user tends to be prone to aggression. The drug received the nickname “crank” because it was often smuggled in the crank cases of vehicles.
Methamphetamine is taken orally or intranasally (snorting the powder), by intravenous injection, and by smoking. A common misconception among users is that some administration methods are safer than others, while in reality all act on the body the same exact way. Methamphetamines damage nerve endings, which cause naturally occurring neurotransmitters—Dopamine and Serotonin—to be ineffective. Because Dopamine and Serotonin are responsible for easing pain (like the pain which comes from drug withdrawal), withdrawal periods are extremely painful because the body does not have its natural pain reliever to administer.
Methamphetamine withdrawal is said to be one of the most painful experiences a human being can endure, and users of the drug should should consider other safer recreational drugs.
Billy started doing crank because he was looking for the ultimate high and did not care about the consequences.