Something to do with death because a Raven symbolizes death.
As he sleeps a bird knocks on his door and makes him extremely paranoid. As he is looking and talking to the bird it says the word nevermore. As the go about the bird keeps on repeating itself and overtime it keeps on repeating itself it causes the narrator to become insane and very angry.
You can infer that the narrator is very annoyed and angry at the bird because it keeps on repeating itself. He is also a little confused to why the bird is doing this.
The tone is very angry. The narrator becomes very angry at the bird for some apparent reason. His attitude towards the bird is whit hate. The bird seems to make him mad.
Throughout the text the narrator becomes crazier and crazier. The bird keeps making him madder and madder but also drives him insane through the text.