The brown rat (Rattus norvegicus), also known as the common rat, street rat, sewer rat, wharf rat, Hanover rat, Norway rat, Norwegian rat and Parisian rat, is a widespread species of common rat. it is a brown or grey rodent with a head and body length of up to 28 cm (11 in) long, and a tail slightly shorter than that. The brown rat is rather large and can weigh twice as much as a black rat and many times more than a house mouse. Rats commonly groom each other and sleep together. Rats are said to establish an order of hierarchy, so one rat will be dominant over another one. Groups of rats tend to “play fight”, which can involve any combination of jumping, chasing, tumbling, and “boxing”.

The house mouse (Mus musculus) is a small mammal of the order Rodentia, characteristically having a pointed snout, large rounded ears, and a long and almost hairless tail. Although a wild animal, the house mouse has benefited significantly from associating with human habitation to the point that truly wild populations are significantly less common than the semi-tame populations near human activity. House mice have an adult body length (nose to base of tail) of 7.5–10 centimeters (3–4 in) and a tail length of 5–10 cm (2–4 in). House mice thrive under a variety of conditions; they are found in and around homes and commercial structures, as well as in open fields and agricultural lands.