Clostridium botulinum is an anaerobic, gram-positive bacterium that secretes an extremely large neurotoxic molecule (900 kDa), which produces food poisoning or botulism. It is now also used in medicine to treat diseases according to Paracelsus's paradigm that the difference between a poison and a drug lies in the dose. Although seven different serotypes of the bacterium are known, type A is the one mostly used for the production of clinical formulations. The surrounding portions have no pharmacological activity and simply act as a protective shield ensuring unchanged toxin absorption from the host's gastrointestinal tract. These surrounding molecules are named accessory proteins and are both hemagglutinin and non-hemagglutinin in nature. Once the toxin has entered the host by ingestion or injection, the biological role of the accessory proteins is largely terminated and the 150 kDa neurotoxin comes into play. Botulinum toxin treatment of mimetic muscles, also termed chemodenervation, requires a thorough knowledge of muscle anatomy.