When he saw that "hideous veiled eye," he became furious. But he warns the reader not to mistake his "over-acuteness of the senses" for madness because he says that suddenly there came to his ears "a low, dull, quick sound": It was the beating of the old man's heart. It is at this point in the story that we have our first ambiguity based upon the narrator's over-sensitivity and madness. The question is, obviously, whose heart does he hear? We all know that in moments of stress and fright our own heartbeat increases so rapidly that we feel every beat.