Rodents are hell-of-a sneaky creatures and can pass through some tiny holes and crevices. Therefore, for a suspected Infestation, the first step is to look at any open cracks and holes that these rodents can potentially squeeze in. When you find an entryway, seal it with a wire mesh, steel wool or any wood or metal that mice cannot gnaw on it. As much as possible, plug up any cracks and holes to ensure that no mice can enter.