What superstition is mentioned in the story?

In "The Black Cat," a short story by famed horror writer Edgar Allan Poe, the narrator realizes that his mental health is quickly deteriorating.  Though he bears witness to his own descent into madness, he feels powerless to stop it. As in all of Poe's stories, we know close to nothing about the narrator/main character, save that something or someone is torturing him.

In this case, it appears to be a black cat, which he...

In "The Black Cat," a short story by famed horror writer Edgar Allan Poe, the narrator realizes that his mental health is quickly deteriorating.  Though he bears witness to his own descent into madness, he feels powerless to stop it. As in all of Poe's stories, we know close to nothing about the narrator/main character, save that something or someone is torturing him.

In this case, it appears to be a black cat, which he fixates on and imagines to be the reincarnation of his previous pet, a cat named Pluto that he irrationally and perversely murdered in a furious rage when he imagined the cat was avoiding him. In fact, the new cat looks exactly like the one that he murdered, save for a white spot on his chest; He is even missing one eye, just as his old cat. It seems to him that the cat has come back . . . perhaps to seek revenge for its untimely death?  

By writing another cat into the story, Poe seems to be drawing from the old superstition of a cat having nine lives. His wife also makes allusions to the fact that cats are supposed to be the reincarnation of witches; to her, they have an otherworldly power. In fact, the name Pluto could even be a reference to the god of the underworld.

This only seems to exacerbate the narrator's suspicion and distrust of the cat. For example, immediately after the narrator cut the eye from his beloved pet Pluto and then hung him from a tree, his house burned to the ground the next day, leaving only a wall with the outline of a cat with a noose around its neck.  The narrator of course tries to rationalize this away but can’t help superstitiously believing that this was an act of revenge for what he had done to the cat.

In addition to that, when the new cat runs across his path, a reference to another superstition about cats being bad luck, he imagines that it’s trying to trip him.  He picks up an axe to kill the cat and accidentally kills his wife instead. He believes that he just needs to get rid of both the body and the cat in order to finally be able to rest peacefully, ironically not realizing how deep into madness he has sunk. When the police discover the body walled up inside the house, the cat is sitting on top of it, a perfect symbol of retribution for the acts committed by the husband.