Edgar Allan Poe uses great characterization, and descriptive word choices in his short story "The Tell-Tale Heart," both of which contribute to the tone of horror and terror. The narrator of the tale is clearly obsessed and slightly deranged; through using such a creepy and evil narrator, who is so frank about his insidious plans, the entire story is cast with a feeling of horror. He admits openly that he had nothing against the old man except for his eye. He finds joy in in the pursuit. For example, consider this passage:
"To think that there I was, opening the door, little by little, and he not even to dream of my secret deeds or thoughts. I fairly chuckled at the idea"
He gloats in his plans, which casts a tone of horror over the story. The way that he claims that he isn't mad, and then describes his awful deed in such minute detail is also very terrifying. His patience, his glee at not being discovered, his manipulation of his poor victim--all of these things add to a really great character that aids in making the tone horrifying.
Poe also uses such great word choices and descriptions in order to create a feeling of horror. For example, the old man's eye was "a pale blue eye with a film over it," which is a creepy image. He uses great punctuation and repetition to describe how the narrator basically stalks the old man. He says things like, "patiently, oh how patiently," and "--very, very slowly," "oh cautiously--oh so cautiously" and "--oh so gently." All of these things increase the suspense. The description of the old man's heart fading, the brutal description of how he got rid of the body--all of Poe's descriptions and word choices aid in creating a tone of horror.
I hope that those thoughts helped; good luck!
Edgar Allan Poe sets the eerie tone of his classic horror short story, "The Tell-Tale Heart," from the opening sentences. The narrator admits that he is mad immediately, although he tries to convince the reader that he is sane, establishing that the story will bring some sort of unnatural actions. Poe uses words such as "nervous," "dreadfully," "hell," and "mad"--in the first paragraph alone--to help set the mood of horror. Most of the story is set late at night and in darkness, symbols of both evil and death. By the third paragraph, the narrator establishes that he has already killed the old man, and Poe draws the reader in and proposes the unanswered questions about how the murder will happen and whether the killer will get away with it.
Other references, such as "the vulture eye" and the imagined loudness of the old man's heart combined with the painstaking steps that the murderer takes before finally making his move, add to the building terror. By the time he kills the old man, the reader can only wonder what will happen next. But Poe merely continues to build one horrible act upon another, first with the matter-of-fact description of the dismemberment, followed by the burial beneath his floor. Just when the reader wonders if this--like "The Cask of Amontillado"--will feature a perfect crime, a knock on the door reveals the police, investigating a scream in the night. The combined madness, nervousness and guilty conscience reveals that the killer's act is not so perfect.