"They can get in around piping and even chew through walls ... of an infestation, such as rat droppings, strange scratching and scurrying noises and gnaw marks on walls or food packaging.

Look for signs of rats and mice: rodent droppings around food, in kitchen corners, inside cabinets, and under sinks; smudges and dark marks near entry points or nests; and chew or bite marks on food, ...