What details in "The Tell-Tale Heart" indicate his fears?
The fear of the narrator is communicated most clearly in the final section of this terrifying story, where the narrator hears--or imagines he hears--the beating of his victim's heart from beneath the floorboards where it is hidden. Note how his fear is communicated through repetition and parallelism:
Oh God! What could I do? I foamed--I raved--I swore! ... It grew louder--louder--louder!
Note how the word "louder" is repeated three times for emphasis, and then parallelism is used in the structure "I foamed--I raved--I swore!" Such language shows the emotional fear that the narrator experiences as he tries to desperately ignore the sound of the beating heart and communicate normally with the police officers. The language and the style that Poe adopts in this section indicates very clearly the fear that the narrator has of being discovered.
Another way in which fear is communicated is through the "evil eye" that the narrator believes the old man whom he kills possesses. The narrator's fear is communicated through the emotional reaction the protagonist has when he sees this "evil eye," as the narrator tells the reader that his "blood ran cold." Here, as in the previous example, the fear of the narrator is communicated through the emotional response that the narrator has when he feels fear. In this case, the sensation of his blood "running cold" when he gazes upon the man's eye signifies the terrible fear that he feels, and that drives him to kill the old man, even though he was pleasant and had done nothing wrong to the narrator.
The first sentence of the narration reveals that the speaker is incredibly anxious and perhaps fearful:
TRUE! --nervous --very, very dreadfully nervous I had been and am.
The narrator claims that the old man he lived with had never done him any harm; however, his blue eye made his blood chill, perhaps with fear, and caused to to take the man's life.
Whenever it fell upon me, my blood ran cold; and so by degrees --very gradually --I made up my mind to take the life of the old man, and thus rid myself of the eye forever.
When the old man hears the narrator in his room, he sits up abruptly, remaining in that position for what is documented as the space of an hour. The narrator reveals that he has engaged in the same behavior, revealing to the reader a state of paranoia.
just as I have done, night after night, hearkening to the death watches in the wall.
I knew the sound well. Many a night, just at midnight, when all the world slept, it has welled up from my own bosom, deepening, with its dreadful echo, the terrors that distracted me.
He then notes that the fear the old man is experiencing is the same fear that would grow within his own being each night. When the officers come by after the old man's death, the narrator's physical anxiety and uneasiness reveals the fear he has of being discovered.
But, ere long, I felt myself getting pale and wished them gone. My head ached, and I fancied a ringing in my ears: but still they sat and still chatted. The ringing became more distinct: --It continued and became more distinct: I talked more freely to get rid of the feeling: but it continued and gained definiteness --until, at length, I found that the noise was not within my ears. No doubt I now grew very pale; --but I talked more fluently, and with a heightened voice. Yet the sound increased --and what could I do? It was a low, dull, quick sound --much such a sound as a watch makes when enveloped in cotton. I gasped for breath --and yet the officers heard it not.
They heard! --they suspected! --they knew! --they were making a mockery of my horror!-this I thought, and this I think.