Botulinum toxin is the most toxic substance known to man. It takes only a small amount of botulinum to kill a human. The lethal dose of botulinum is estimated at 70 micrograms for an adult human. By comparison, the estimated lethal dose of cyanide is 200,000 micrograms. Botulinum toxin is produced by a bacteria called Clostridium botulinum. People are exposed to this poison when they eat contaminated food, or if the bacteria gets into a deep wound (the sickness that results from this toxin is called botulism). Botulism can cause paralysis of muscles, including the ones we use to breathe.