If I were to change anything in Edgar Allan Poe's "The Black Cat," I think that it would have something to do with the narrator's wife. The main character's change in character with regard to the animals is gradual, but noted by the speaker. It comes as no surprise, then, when he becomes so obsessed about their cat that he kills it. The narrator speaks of an early love for animals:
I was especially fond of animals, and was indulged by my parents with a great variety of pets. With these I spent most of my time, and never was so happy as when feeding and caressing them.
When the narrator meets his wife, this is something they have in common, and they have pets in their home. One is a black cat, and the author praises the animal, Pluto:
This latter was a remarkably large and beautiful animal, entirely black, and sagacious to an astonishing degree.
The narrator favors the cat above all the other pets. However, after several years, he begins to drink heavily and becomes angry and cruel—especially to the pets. First he grievously injures Pluto, and then, with a perverse spirit, kills the cat for the simple pleasure in this sinful act.
Only once in this entire segment regarding his change in character and behavior does he speak of mistreating his wife, and at that, it is a small, solitary entry. He does, however, give a great deal of attention to the animals. Once Pluto is dead, the narrator discovers another cat very similar to Pluto, who follows him home for a drinking establishment. The man expects he will feel differently about this cat, but soon comes to loathe its very existence. In this long description of the speaker's feelings, as well as his hesitancy to harm this cat, the wife is only mentioned twice: once in how she took so quickly to this new animal. And again as to how patient she was under the verbal abuse she received from her husband.
What throws me off is that the wife is really a secondary character whose only purpose seems to be to provide a victim for the man that moves the plot line forward: for to kill a cat, a man would not be punished. But should he kill a wife, his fate would be sealed. And he does kill his wife when she interferes with his attempt to kill the cat:
...this blow was arrested by the hand of my wife. Goaded, by the interference, into a rage more than demoniacal, I withdrew my arm from her grasp and buried the axe in her brain. She fell dead upon the spot, without a groan.
Obviously, as the cat eventually gives away the place where the narrator has hidden the body of his dead wife, exacting a "cosmic" revenge upon him for his murderous behavior, the wife's demise seems present only to place the narrator in the circumstances needed to sentence him to death. While the majority of the story is about the narrator and the animals, the sudden death of his wife seems too sudden and contrived. This I would change: writing of her more, or not at all.