These parasitic flatworms are the stuff of legend evoking grotesque images of starving humans who fail to satiate their hunger despite constant eating. But tapeworms are the real deal. While they do not generally cause symptoms like extreme, uncontrollable hunger, they can range from 0.04 in. (1 mm) to 50 ft. (15 m) in length and live inside the liver and digestive tracts of all types of vertebrates, including humans, domestic animals and fish. Tapeworm infections are caused by eating raw or undercooked meat from infected animals, and most people don't even notice that they are infected until they pass pieces of the worm in their bowel movements. Tapeworm infections can be treated with medication and are often curable.