Bread afflicted by a bacterial infection, typically Serratia marcescens, that stains the crumb with startling blood-red patches. The phenomenon terrified medieval communities, who interpreted the apparent bleeding as miracle or omen, most famously in Eucharistic miracle legends. The bacterium thrives in warm, moist conditions and produces the red pigment prodigiosin, turning innocent loaves into objects of supernatural dread. Modern microbiology solved the mystery, and improved hygiene and storage have made it rare, though it still appears occasionally in bakeries with sanitation lapses. The story is a perfect parable of food microbiology: a natural phenomenon, frightening when unexplained, manageable once understood, and a reminder that bread’s very nourishment makes it an excellent microbial medium.