This is the key sentence:After the tragic events of The Third Policeman, many decades passed while the Mathers mansion lay vacant and unused for literary purposes. At last it passed into the possession of Lucy's family (and no credit redounds to their realty dealer who failed to warn them of its history). Evidently what was once Fox was still in residence within the walls, but after such prolonged exposure to omnium's mutagenic rays he had not only changed species but also undergone a process of corporeal fission: However, the media exaggerate the scale of the mammals-in-the-walls problem. It is totally unfair. Many families have insectivores or monotremes or large ungulates occupying the cavities hollowed out within the walls of their house, and find them to be perfectly congenial neighbours.** It is just one or two species of canidae who give all the other mammalian families a bad name.
Among the canids, Japanese raccoon-dogs or Tanuki are notable for their nuisance potential. Judging from the shape-shifting protean properties of their testicles, Tanuki have their own supply of omnium.
If you have dholes in the walls it is possible that you are inhabiting an H. P. Lovecraft story.
* Sixteen and eightpence in the pound with thruppence in the pound for bad yellow water that I would not use and fourpence by your kind leave for technical education.
** Homes where