Fleas and rats spread the Black Death. Firstly, the rat had the plague, next, the flea drinks the rat’s blood and gets the disease. Thirdly, the flea sits on a person and bites the person’s body, in that process, the flea vomits, puking the disease to the person. This shows how easily the Black Death could spread throughout Europe. Once the humans caught the plague, they showed a series of symptoms.