Explanation: Just to elaborate a little on the answer, it can be added that by hinting at what may happen in the future—Fortunato will eventually die, and indeed not of a cough, but by being buried alive—Poe is employing foreshadowing. Fortunato says that his cough will not kill him, to what Montresor replies "true—true," since he well knows that that's not going to be the cause of his death. An humiliated and vindictive Montresor will bury him alive. This technique keeps the reader engaged and interested.
