Quote 7
Hearken! and observe how healthily – how calmly I can tell you the whole story. (1)
In some ways, the story is told rather calmly, though "healthily" is a bit of a stretch. There is control in the narrative. This control is maintained in part because the narrator doesn't tell "the whole story," but select bits and pieces of it.
Quote 8
And then I thrust in my head. Oh, you would have laughed to see how cunningly I thrust it in! (3)
Go ahead. Snicker. Get it out of your system. We had to put these here because it has the word "cunningly" in it. This line is so silly it borders on hilarious. Good old comic relief. Clever Poe.
Quote 9
To think that there I was, opening the door, little by little, and he not even to dream of my secret deeds or thoughts. (4)
Such sad lines. His idea of being cunning seems so pathetic, and so creepy and destructive. We also wonder why the narrator is so sure the man doesn't suspect him. Is it because of the narrator's cunning, or the old man's lack of it?