Mercury is a toxic liquid metal that poisons the nervous system, the stomach, the intestines, and the urinary system. It can enter the skin through inhalation of the vapor, ingestion, and injection. Mercury can come in three forms: As an element, as an inorganic salt, and as organic compounds. Methylmercury (CH₃Hg) is the most dangerous kind of mercury because 90% of the methylmercury ingested will be absorbed, while no ingested elemental mercury will. Almost all seafood have traces of methylmercury.