Mouse poop looks like small, dark brown or black granular pellets that are about a ¼ inch on average. They are commonly mistaken for feces that belong to other rodents or cockroaches, which is why identification is sometimes difficult. Mouse droppings are small, thin, pointed pellets that have tapered ends and look like seeds or small dark grains of rice. They are often found in clusters and may look similar to small pellets. Fresh droppings are a darker black color and have a moist sheen, while older mouse droppings usually fade to a light brownish-grey color and are very hard and dry. The color may lighten some with age, but dark brown is still what you’re looking for to detect mice poop. Rat droppings tend to be much bigger than mouse droppings, which is the easiest way to tell the difference. Mouse poop can contain bacteria and viruses that are harmful to humans, so it is important to clean it up properly and take precautions to avoid infection.