Cyanide is a highly toxic substance, including hydrogen cyanide, sodium cyanide, potassium cyanide, ammonium cyanide and acrylonitrile. Fumes of hydrogen cyanide and acrylonitrile can be quickly absorbed through the skin and respiratory tract. Cyanide is widely used in industry. The kernels of many fruits contain amygdalin, which can be converted into cyanide after entering the human body. Among them, bitter almonds have the highest content. Cyanide can cause tissue cell hypoxia, energy metabolism and other disorders, causing "intracellular asphyxiation", while blood oxygen saturation is not affected and the blood remains bright red. The central nervous system is affected first, and paralysis of the respiratory center is the main cause of death from hydrogen cyanide poisoning.