TapeWorm
It is a parasite that absorbs predigested food. There is no need for a tapeworm to have a digestive system when it uses the human digestive system for itself. So it can gain all of the nutrients it needs by taking in the pre-digested food. It's basically what we call a parasite. You get a tape worm from eating raw food, just like the delicious filet tartar, or simply some sashimi, or food that is already infected. Once the tape worm is inside, it can move anywhere in you body including intestines, skin, central nervous system, and bone marrow. It would begin the process of gathering nutrients by latching onto the intestinal wall using an aparatus at the top of its head known as a scolex Licorice root, agrimony, marshmallow and wormwood are herbs that can be used to kill this worm. You can also pass the worm through the anus to get rid of it. Presumably, a tapeworm's diet consists of any pre-digested food that a human consumes, so the tapeworm actually has no preference in what it eats.
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