"Adoption Process" is a short story by Phil Geusz. It appears in the mainstream collection Twisted Cat Tales, edited by Elizabeth Schrader. The tale is about a young homeless man who wants to become a cat, narrated by the small-time artist who "adopts" him off of the street. At first, the elderly man is convinced that he has accepted a lunatic into his home. Slowly, step by step, the young man eases the narrator into accepting him as a feline. By this point, both have clearly traveled far beyond the normally-accepted limits of sanity.
"Adoption Process" includes disturbing scenes of self-mutilation and psychological manipulation.