Stephen Ratcliffe, writing in Modern Language Studies regarding the murder of the King suggests that "this manner of death-by-poisoning-through-the-ear followed by this ear/eyewitness account of that death are particularly significant, especially in a play that pays so much attention to acts of speaking and of listening." Where do you find evidence in the play of the importance of speaking and listening?
Hamlet is desparate to get his mother to listen to him during the closet scene in Act 3. He seems to have finally made his point when she exclaims, "Oh speak to me now more! / These words like daggers enter in mine ears. No more sweet Hamlet." She obviously just wants to shut him up, but the words against her behavior are a poison to her, and in the end, she does listen and try to protect Hamlet from Claudius.
Let's not forget that Hamlet's "The play's the thing wherein I'll catch the concience of the king" is about listening and internalizing one's own emotions and guilt. Listening is also a factor in Polonius's death in that he was behind the wall listening to Hamlet and Gertrude.
The whole exchange between the soldiers, Horatio, and the Ghost, then between the Ghost and Hamlet is all about speaking and listening.
The Ghost refuses to answer Horatio and the soldiers when they entreat him to speak. He is waiting to talk to Hamlet, so it is apparently quite important that he says what he has to say to the right person. The Ghost might be listening to them, but he's not doing any talking at this point.
When Hamlet arrives, the Ghost tells him what he can and cannot talk about - He can't talk about the afterlife ("But that I am forbid to tell the secrets of my prison house..."), but he can tell Hamlet the circumstances of his death. But even before telling him everything, the Ghost says,
"List, list, oh, list!"
I think it's important to note here that Shakespeare didn't use exclamation points as often as we do today. In fact, many modern editions of his plays have way more in them than the First Folio had (I've started using the Arden editions because they stick to the Folio or the earlier Quartos with regards to punctuation.). So I think it's critical here that not only is the Ghost telling Hamlet to listen - he's EXCLAIMING the importance of listening.
Finally, after the exchange is done and the Ghost needs to leave (the cock is crowing, after all), he still has to tell the men to swear on Hamlet's sword not to reveal what they've seen or heard. Swearing, speaking, listening - it's all critical to this scene!
Good points. Two others are Polonius' speech to Laertes before he goes to school--never a borrower or a lender be, etc., etc.
Also, both Laertes and Polonius give advice to Ophelia regarding Hamlet and his behavior toward her.
My students are intrigued by this method of poisoning, first of all, but as they read the play, I'm always pleased that they note the many supporting examples of figurative poisoning by ear. Polonius' directions to Reynaldo to spy on Laertes with "a bait of falsehood" to gain "a carp of truth" indicate that the servant is to use half-truths about Laertes' apparently less-than-decorous behavior. Hamlet's "get thee to a nunnery" speech to Ophelia to drive her away by insulting her by his crazy talk and his crude conversation prior to "The Mousetrap" are two examples of a different kind of poisoning. He isn't trying to gain information here; instead, he deliberately offends her. The results in virtually all instances of either of these kinds of examples are negative.
From recognition of these and other examples, students typically make a connection to the damages incurred by any kind of malicious gossip, ad hominem attacks, and even inadvertent, hurtful comments. Then they begin to understand why Shakespeare used this method of murder. Who cares if we question the likelihood of real snakes in a Danish winter (as Branagh depicted the murder scene)? A snake is a snake. Just another of those minor details (like Hamlet's age), according to Bloom, that Shakespeare wasn't concerned about.