If one piece of bread is moldy are the rest bad?

Not always. You can find mold on some food items and cut off the piece that has the mold on it. However, if the mold is extensive, it is best to discard the entire piece of bread. Mold can spread quickly and easily, so it is important to err on the side of caution. Additionally, some types of mold can produce harmful toxins that can make you sick, so it is important to avoid consuming moldy food.