Crank" is a slang term for someone infected with the Flare virus. "The Gone" is another term used for a stage of viral progression in those infected, when a person is past humanity and has lost what sanity they had.
In the film series, Cranks are depicted as zombie-like creatures with strange vine-like growths protruding from their bodies. The book series clearly defines the differences between Cranks and regular zombies, however, as Cranks remain alive and somewhat have the ability to speak.
The Gone is a term referring to the point of no return for a Crank. Usually, it is used as part of the term "past the Gone." When a Crank is past the Gone, he or she will be uncurable and will turn to animal-like behaviour and cannibalism. When past the Gone, they will be unable to control their own thoughts or movements.
The Flare (virus VC321xb47) is a man-made disease. It is a virus that slowly eats away at the brain, eventually turning its victims into bloodthirsty and irrational humans who consider cannibalism an everyday objective. People who have the Flare are commonly called Cranks. Every large remaining city in the world has a special holding place for Cranks known as a Crank Palace.
After the Sun Flares, the Post-Flares Coalition decided that there were not enough resources for the remaining population, and they searched for a means of population control that would eliminate large numbers of people quickly and humanely. The Flare was discovered by Katie McVoy, a scientist of the Post-Flares Coalition (PFC), after she researched the biological weapons that AMRIID had in containment. McVoy believed that the disease worked quickly and painlessly to shut down the brain of its victim and that the infection rate would slowly weaken as it spread to different hosts, eventually stopping altogether. However, after Chancellor John Michael approved the systematic release of the disease, its true effects soon became apparent.
The public was led to believe that it was freed from containment when the Sun Flares destroyed parts of the earth. Meanwhile, WICKED was formed in an effort to find a cure for the dangerous disease. A small percentage of the population, most under the age of twenty, were labeled as Immunes, people who were not affected by the Flare. WICKED attempted to use the Immunes to find a cure by looking at how the brains of the Immune people reacted to certain situations, as well as the physical make-up of the brain of the Final Candidate. Immunes were very rare, comprising less than 1% of the Earth's population, and as such, they were given the nickname "Munies" by those not immune out of spite and envy.
There are various stages of the Flare. Early on in the disease, a Flare-infected person will often feel "off" somehow, exhibiting symptoms such as sudden mood swings, paranoia, poor balance, headaches that get worse as time goes on, irrational anger, and aggression. These symptoms gradually worsen, stripping the victim of their humanity and turning them into a demented, cannibalistic, zombie-like lunatic. When they have gotten to the point where sanity is completely lost, they are referred to as being past a stage known as "the Gone." Those who are past the Gone often have horrifying injuries, presumably gained through fights with other Cranks. An example is a Crank in The Scorch Trials that is bereft of his nose.
An extremely active brain, often triggered by stress, will quicken the rate at which the virus does its damage. Due to this, a treatment known as the Bliss was created to sedate a person's senses and neural activity. However, the drug is only affordable by the extremely wealthy, due to its high price, and simply delays the inevitable, thus not making it a cure. The Bliss slows the brain's activity, making a person seem more relaxed in various situations. It is quite easy to tell if a person has been taking the drug.
The second film portrays Cranks, victims of the Flare, as black-veined, long-armed zombie-like creatures. Strange vine-like growths protrude from their bodies, and they do not seem to be capable of speech. Unlike in the novels, however, Cranks seem to able to transmit the Flare to others (possibly Immunes, even) via forms of physical contact, such as scratches.
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