The Black Death, which exploded in Europe thanks to religious zealots who were trying to eradicate the Devil's servants.

Although the disease originated in China, it spread rapidly and widely, killing up to 60% of Europe's population between 1348 and 1350. During the years leading up to the Black Death, many European Christians began killing cats because they were told that cats were vessels for Satan's spirit. Their efforts to ward off bad luck in this manner left no defense against the black rats that came over on Asian merchant ships, bearing the Oriental rat fleas that spread the plague.