Ergot fungus is a type of fungus that primarily infects cereal grains, especially rye. It produces dark, elongated structures called sclerotia, which can replace the grain kernels. These sclerotia contain toxic compounds known as alkaloids, which can be harmful to humans and animals if ingested. Historically, consuming bread made from infected rye led to a condition known as ergotism, characterized by symptoms like hallucinations, convulsions, and gangrene. Today, strict agricultural practices help prevent ergot contamination, ensuring that grains are safe for consumption.