Define the metaphor and explain the two-part comparison in Lady Macbeth's line:"The raven himself is hoarse/That croaks the fatal entrance of Duncan/Under my battlements" (1.5.39-41).
In Shakespeare's Macbeth, Act 1.5, the raven, a bird of evil portent and usually associated with death, is hoarse from calling out the arrival of Duncan. The idea is that the raven, a harbinger of death, is so excited that it has gone hoarse from proclaiming Duncan's arrival so vigorously. Someone, or something, goes hoarse from talking too much, not from talking too little.
The "fatal" in the line has two meanings: fatal for Duncan, of course, but fatal also in the sense that it is fate or destiny that Duncan will die.
In short, Lady Macbeth performs what we, today, call a pathetic fallacy. She projects her own excitement on to the raven, seeing the raven as just as excited by the idea of Duncan's death as she is.
The passage, then, certainly is anthropomorphic. Lady Macbeth attributes human behavior to a bird.
But, unless birds are incapable of becoming hoarse, the lines do not constitute a metaphor. If birds can't become hoarse, then the raven is being compared to a person that yells too loudly for too long, and therefore becomes hoarse. Specifically, the bird is being compared to the person who would announce Duncan's arrival at the castle. But if birds can become hoarse, then the lines aren't metaphorical.
I don't know anything about bird anatomy, so I can't definitely say one way or another, but the lines don't appear to be metaphorical. They are anthropomorphic, but not metaphorical.
In Act 1, Lady Macbeth prepares herself to go through with helping Macbeth murder King Duncan. The King arrives at Macbeth's home under the pretense of a dinner party, but Lady Macbeth and Macbeth have already planned the murder. All care is under the charge of Lady Macbeth, and the atmosphere of the home has darkened under her and her husband's plan. The raven, normally a loud bird, cannot warn King Duncan of the horror that awaits him. His entrance to the home is doomed. So, the metaphor states the inevitability of King Duncan's death at the hands of Macbeth.