Flash cloning

Flash Cloning is a medical process used by the UNSC whereby human body parts are cloned. This usually involves a sample of a person's DNA which is used to grow a clone of an organ or body part, which can then be transplanted into the person the DNA came from. This way, organ transplants are faster and easier and the rate of success is far higher. Usually the organ is programmed to grow at an accelerated rate, then to cease rapid development when transplanted into the person. Therefore, the organ grows quickly and functions properly and efficiently. Since the organ contains the same person's DNA, there is no threat of rejection by the body.

Human Cloning
Flash cloning humans is imperfect and is illegal for civilians to flash clone. Doing so would result with harsh punishments for violators. An embryo is taken and developed a hundred times faster than it would have naturally, becoming something different than it would have been. Many anomalies appear because flash clones are forced to develop too quickly. Flash clones have none of the memories of their hosts, including the natural behavioral training most humans get observing people while growing up. They can be trained with intensive therapy, but after a month or two, they start to degenerate from metabolic instability in a process called "Metabolic Cascade Failure" until they die from various neurological and physiological diseases.

After the future SPARTAN-IIs were kidnapped from their homes, they were replaced by flash clones, intended to explain the sudden disappearance of the Spartan II candidates. Though the flash clones quickly died, they had succeeded in their purpose - to draw attention away from ONI.