The Hamsters Next Door is a group of five is the any kind of species of Hamsters. In Operation: P.I.A.N.O., a hamster was used as a temporary replacement for Numbuh 4 when he is injured. Then when the whole team thus creating Hamsters Next Door. In Operation: H.A.M.S.T.E.R., an episode focusing entirely on them, they fight the DCFDTL's pet cats and feline counterparts, the Sinister Felines from Atop the Litterbox. They are the pet hamsters of the Kids Next Door.