The above-referenced passage from Poe's "The Tell-Tale Heart" is certainly interesting to analyze. We have an unreliable narrator telling us how cunning he is while carrying out a murder. Then we also have Poe creating tension and suspense through the actions and thoughts of that narrator. Should we believe what the narrator says about himself and what happened? If not, what can the reader determine is true in the story? The answers to these questions are found within each reader's mind as he or she reads and makes conclusions based on the evidence within the text.
However, while the narrator attempts to prove his prowess and sanity throughout the story, he only winds up proving how insane he is. It would be comical if it weren't for the fact that a poor, innocent old man dies as a result. But if one were to analyze the quoted passage above, what would one find?
First of all, the narrator thinks that he is patient and calm, but also cunning and clever by standing still for one hour just within the door of the old man's room. No, maybe that's just creepy! And who knows, maybe that's just hyperbole and the killer wasn't really standing there for a whole hour. Whatever it is, hyperbole or truth, it's still showing that the murderer isn't sane. But this scene is clever on Poe's part because it does cause one to wonder how it would feel to have a weirdo standing in one's room for an hour, and that's perfect for the story because that is what creates tension.
Then there's the fact that the old man is also sitting up in his bed in terror for a really long time. The narrator seems to be proud of himself to create such terror, but through the old man's actions one might feel pity for him and remember a similar time of terror in one's own life. Again, turning back to the narrator, one might feel anger for scaring the poor old man in such a way—and right before killing him, too! Sane or insane?
Finally, the passage quoted above shows just how frail the old victim is because he lets slip a frightened moan of terror. This moan shows that he knows someone is in his room and hasn't left. It is probably at that point that the old man realizes what is going to happen to him and his fate is fixed.
Whether the reader believes the murderer is sane or not, the fact of the matter is that Poe skillfully creates tension and suspense in this story through language and without the help of background music or jittery camera angles like in the movies. Being one of the first to create such compelling and frightening thriller and horror stories, Poe set the bar high for others who came after him.