Two of Edgar Allan Poe's best short stories are "The Black Cat" and "The Pit and the Pendulum." Each of the stories is told from a first person perspective. Each of the narrators is telling the story after it takes place, but from opposite ends of the spectrum. The murderer is telling us his story from prison before his death and the prisoner tells his tale after escaping death at the hands of the monks. In "The Black Cat" the narrator says he is placing the events before the world plainly, without any exaggerations. In "The Pit and the Pendulum" however, the narrator's tale isn't as believable because he's telling it after he narrowly escaped a horrible end, which means that in retrospect he knows what is going to happen and could exaggerate some of his feelings. Overall, I believe that the first person perspective is effective in that it makes the story seem more realistic.
Death is described in a way that is particularly gruesome to me in both stories. Instead of simply writing that the wife was murdered with an axe, Poe writes that the narrator buried the axe in her head. That puts a nasty picture in my mind and makes the story seem that much more realistic. Having that image also makes the story more personal. In "The Pit and the Pendulum," the blade swinging back and forth is terrifying to me. Thinking of it very slowly cutting through clothes, then flesh, then bone, until it finally reaches the heart sends chills down my spine, which is what Poe was going for. His good descriptions make the reader able to feel what the narrator is going through.
The biggest difference between the two, in my opinion, is that the endings are totally different. In almost every Poe story, somebody dies at the end or is discovered to be a murderer, but in "The Pit and the Pendulum" the exact opposite happens. The narrator is saved from the certain death the whole story described. "The Black Cat," on the other hand, has the more typical Poe ending.