Crucial to understanding this question is the fact that it is the speaker who narrates this tale. Poe is a master in using the unreliable narrator to present unstable personalities, who are either mad, haunted or worse, and this speaker in "The Raven" is no exception. Consider the situation. The speaker is a weary student, studying in the early hours of the morning and is haunted with grief for his former love who has died, Lenore. Hearing the rapping sound against the shutter, he opens it and the raven flies in. The speaker begins to ask it questions, to which it always replies "Nevermore." However, it is the speaker that is clearly driving himself into ever-greater depths of depression and madness by his questions, knowing at some level that the raven will always respond in the same way:
"Be that word our sign of parting, bird or fiend!" I shrieked, upstarting -
"Get thee back into the tempest and the Night's Plutonian shore!
Leave no black plume as a token of that lie thy soul hath spoken!
Leave my loneliness unbroken! - quite the bust above my door!"
As his questioning becomes ever-more frantic, we can see that he is almost delighting in self-torture as he leads himself from initial curiosity to horror. This poem explores the dark side of human nature, what Poe himself referred to as "that species of despair which delights in self-torture." A psychologist would probably say that the speaker is projecting (putting onto) the bird whatever his own wild, frenzied and grief-stricken imagination throws out.