Can you tell me what occurs if you eat meat that is not fully cooked?

Varies: It depends on the meat and any potential contamination or infestation. Steak tartare is raw beef, that is examined closely for contaminants and bacteria. Cooking kills germs, larva, worms, etc. If the meat is clean, it is safe. The problem is, modern day processing does not remove the contaminations, so cooking is the best way to prevent disease.