As I love to mention, apropos of Poe's poem "The Raven", ravens can be trained to talk, the way a parrot can.
So the actual events of The Raven are plausible - namely, a raven shows up, flits about a guy's library, answers every single question with "Nevermore", and fills the guy's heart with despair.
They are plausible if - someone trained a raven to say "Nevermore".
My friend, William Dale, asked me who would have done such a thing, and a backstory came to me.
The bird trainer was a young woman named Ava, who was sweet on the poem's narrator, but who was frustrated by his obsession with once again seeing the lost Lenore. She was just trying to move him to acceptance of the fact that Lenore wasn't coming back.
Ava actually wrote a short poem explaining her efforts:
Since that guy was so obsessive, and found omens so impressive,
I resolved to train a bird to speak and flit but not to soar,
Patiently I kept repeating, like a drum that's always beating,
Like a sheep that keeps on bleating, just one phrase forevermore -
And my tongue grew tired, I tell you, but I kept on, and I swore
That bird would say "Nevermore".