"You fancy me mad. Madmen know nothing. But you should have seen me. You should have seen how wisely I proceeded—with what caution—with what foresight—with what dissemination I went to work!" —Edgar Allen Poe (from The Tell-tale Heart)
In this poem, the speaker tells the reader that he is sane shortly before describing himself as a "madman." The irony of this is frightening in the sense that the reader understands that the story has occurred, and they must sit hopelessly awaiting the end. That reader understands that a man who insists on being sane, yet has done such a terrible thing, cannot be so. The speaker is clearly insane, so the reader, being sane (hopefully) is fearful because of this fact.
Answer: The reader knows that madmen are unpredictable and difficult to control.
Hope this helps!
