Teniasis is the medical term for infestation of the human intestine with a tapeworm — most often Taenia saginata from beef or Taenia solium from pork. People become infected by eating raw or undercooked meat containing the larval cysts; the worm then grows in the intestine, sometimes reaching several metres, absorbing nutrients through its skin. Many infections cause few symptoms beyond mild abdominal discomfort or the alarming passage of segments, but the pork tapeworm’s larvae can migrate to the brain and cause serious disease. Prevention is straightforward food safety: cook meat thoroughly, freeze it adequately, and maintain meat inspection. Treatment is with antiparasitic medicines that kill the worm.