Upon intake of cyanide by mouth, the acid of the stomach converts the cyanide into hydrogen cyanide, which is volatile. Not everyone is able to detect the smell of hydrogen cyanide, however. Although cyanides are highly poisonous, they are by no means the most toxic substances known. The poison acts by tying up all the body's hemoglobin, making it unavailable for transporting oxygen. Sublethal doses cause dizziness and headaches, similar to cases of carbon monoxide poisoning, since carbon monoxide also reacts with hemoglobin.
Many natural substances contain hydrogen cyanide in a combined form, called amydalin.
Peach pits and bitter almonds are examples. Combined cyanide is also responsible for the toxicity of the leaves of the yew tree, and of sorghum in the early stages of its growth. Mature sorghum contains almost none of the relevant compound, and is used as an animal feed. Today, cyanides are no longer manufactured from dried blood. Sodium cyanide is made in a series of reactions involving limestone, carbon, sodium carbonate and nitrogen from the air.