Creatinine is a toxin produced during the metabolism of meat in our body. Therefore, people with lots of muscles or who eat lots of meat always have a relatively high creatinine level, but it usually fluctuates in the normal range: 0.5-1.3mg/dL.
comet definition An object that enters the inner solar system, typically in a very elongated orbit around the sun. Material is boiled off from the comet by the heat of the sun, so that a characteristic tail is formed.
Comets are usually made of frozen water and supercold methane, ammonia and carbon dioxide ices. Those are mixed with rock, dust, and other metallic bits of solar system debris. Comets have two tails: a dust tail (which you can see with the naked eye) and a plasma tail, which is easily photographed but difficult to see with your eyes.