The term 'sewer rodent' is a reference to the RAT, which is a three-letter word. Rats are small mammals that belong to the genus Rattus and the subfamily Murinae. They are omnivorous and have become a major pest in many parts of the world due to their ability to live in close proximity to humans. Rats are known to inhabit sewers and other areas where food is plentiful. They can spread disease and cause damage to property, making them a nuisance to many people.