Dark fuzz that grows very rapidly on bread is an example of?

Dark fuzz that grows rapidly on bread is most likely mold.

Mold is a type of fungus that thrives in warm, moist environments, making bread a perfect breeding ground. The fuzzy appearance is actually a network of hyphae, which are the thread-like structures that make up the mold colony.

It's important to note that not all mold is black. It can come in various colors, including green, white, and even pink. However, black mold is a common type that appears on bread.

If you see mold on your bread, it's best to throw it away, as it can produce toxins that are harmful to humans.