1) In this sentence, the narrator opens the door with more caution than before, but still makes a noise when he tries to turn on the lantern. The old man immediately wakes up and gets scared. To understand this sentence, you need to know the context of the story and the sequence of events leading up to this point.
2) The old man's eye is open, which angers the narrator and frightens him. The narrator stays completely still, not moving a muscle, and doesn't say anything. The use of adjectives and verbs in this sentence highlights the narrator's emotions and reactions to the situation.
3) The adverbs in this sentence emphasize the narrator's efforts to convince the reader that he is not insane, and it also emphasizes the careful planning and execution of the brutal crime. To understand the purpose of these adverbs, you need to consider the narrator's motive and state of mind throughout the story.
4) The narrator starts to hear the beating of the old man's heart, but it is actually happening within the narrator himself. This detail is mentioned earlier in the story, establishing the narrator's hypersensitivity to sounds and sensations that others cannot perceive. To understand this sentence, you need to recall the earlier information about the narrator's heightened senses.
5) This sentence mentions how our own heartbeats increase rapidly in moments of stress and fear, and how we can feel each beat. The narrator not only kills the old man but also hides his body beneath the floorboards in the old man's room. The irony lies in the fact that the crazy man was actually the old man's caretaker. Understanding this sentence requires awareness of the common physiological response to fear and the twist in the story with regards to the caretaker's role.