What clues does Edgar Allan Poe gives to imply that the raven is a symbol rather than a literal creature?

In "The Raven," Edgar Allan Poe provides clues that the raven is a symbol through its supernatural abilities, its repetitive speech that emphasizes despair, and its role in tormenting the narrator's psyche. These characteristics suggest that the bird embodies deeper meanings related to grief, loss, and the narrator's mental state, rather than being a literal creature.