We are doing a renovation. Builder exposed a sewer and left it open. We now have a rat! It might be more than one but I don't see tons of drones so not sure. It had made a nest and tools the bait I bought back to it. It had chewed one corner of a bait block but the rest looked intact. It isn't dead though as I've heard it both nights since. I don't think it's an infestation as not many droppings were in the nest. How would I tell?