Edgar Allen Poe's "The Tell-Tale Heart" and "The Black Cat" were written around the same time, thus explaining their common theme. In both stories, the theme of Insanity is present by which the narrator has a certain obsession, engages in a murder, and displays a false confidence. These three matters straightforwardly depict the narrator's characteristic of being insane in both short stories. .
In both of Poe's stories, the narrators have undeniable obsessions that they can not control. In The "Tell-Tale Heart" the narrator, who claims he is not insane, has an obsession with the eye of the old man he is living with. He despised this eye and would sneak into the old man's bedroom every night for a week around midnight to behold his eye. The narrator hated this eye and wanted to destroy it. However, he did not look down on the old man, it was the vulture-like eye that the narrator disliked. "And this I did for seven long nights-every night just at midnight-but I found the eye always closed; and so it was impossible to do the work; for it was not the old man who vexed me, but his Evil Eye" (Poe 139). In "The Black Cat" the narrator obsesses over his black cat named Pluto. Of all his other pets, this was his favorite pet and playmate. He spent most of his time with this cat and it followed him wherever he went. Later in the story, the man would exhibit awkward and greedy feelings and stay out late heavily drink alcohol. Pluto would try to stay away from him when in this state, resulting in the narrator seriously hurting him in an attempt to erase those feelings. "I took from my waistcoat-pocket a penknife, opened it, grasped the poor beast by the throat, and deliberately cut one of its eyes from the socket" (Poe 13). The narrator unwillingly hurt his cat, and later regrets his actions. This action further proves his insanity as he obsesses over the cat.
Furthermore, murder comes into play when dealing with the theme of Insanity.