It was Carrot who'd suggested to the Patrician that hardened criminals should be given the chance to 'serve the community' by redecorating the homes of the elderly, lending a new terror to old age and, given Ankh-Morpork's crime rate, leading to at least one old lady having her front room wallpapered so many times in six months that now she could only get in sideways.
Terry Pratchettat least nine-tenths of all the original reality ever created lies outside the multiverse, and since the multiverse by definition includes absolutely everything that is anything, this puts a bit of a strain on things. Outside the boundaries of the universe lie the raw realities, the could-have-beens, the might-bes, the never-weres, the wild ideas, all being created and uncreated chaotically like elements in fermenting supernovas. Just occasionally where the walls of the worlds have worn a bit thin, they can leak in.
Terry Pratchett