Answer:
The narrator of Edgar Allan Poe's story opens the tale by insisting that he is not only sane, but also stronger because of a recent illness that has rendered his "mind ... feelings ... senses stronger, more powerful." In particular, he claims that his "sense of hearing especially became more powerful." A thoughtful reader will understand right away that the narrator's protestations of his sanity are a red flag that something is wrong with his thought process. Generally speaking, people who are well-adjusted and healthy don't need to verbally affirm their mental fitness. The narrator, however, assures his audience that he will, in fact, prove "how healthy [his] mind is."