In Poe's short story "The Tell-Tale Heart", the writer uses the horror theme and the dark side of humanity to show violent tendencies exist in the human heart. Poe believed that a piece of writing should produce a single effect on the reader, and was the first to write detective and horror stories which certainly lend themselves to a single effect. In this story,the narrator waits at night. listening for the old man, carefully carrying through his plan to kill him. He even says that he was never so good to the old man than the week before he killed him. The narrator of the story insists that he is sane while the reader knows that he is truly insane After killing the old man, the narrator can still hear the beating of the old man's heart even though no one else can which shows the effect of his guilty conscience. When the police arrive to check out the report of a scream, the tension builds and the narrator becomes more and more agitated, finally screaming out his guilt. Poe doesn't have his just say that he is guilty, he has him scream it out all the while the reader is wondering if the narrator is going to kill the police because of his great guilt. I believe that this story is the classic case where Poe uses his single effect to show that violence exists in the human heart and only needs our consent to be used as a weapon.