These slimy things you can get in your intestine and you will not even know if they are there until they appear dangling alongside your feces. Aside from diarrhea and discomfort, it is hard to diagnose and you will get them from undercooked meat or freshwater fish.
They are called protozoan parasites. It is one such protozoan that causes the disease toxoplasmosis. The infections with toxoplasmosis usually causes no symptoms in adult humans except if the infected individual is already weakened then the parasite can cause numerous illnesses and it can cause damage throughout the whole body. This can be found in any warm blooded animal but in order to avoid it, you just need to practice proper hygiene techniques like not eating raw meat or ingesting food or water from fece-ridden areas. A number of studies have actually suggested that infection may cause personality changes but sometimes there is limited evidence.
Credits to neurosciencenews.com