Is Hamlet reacting with any degree of surprise? Or is he taking this first clear proof of “treachery” as an opportunity to inform everyone about the plot he’s understood all along?

In calling for a lockdown, Hamlet is looking to trap his “rat,” Claudius, once and for all. See also, in 3.1: “Let the doors be shut upon him, that he may play the fool nowhere but in’s own house.”

Osric’s concern for the queen and Laertes (rather than Hamlet) further hints that he’s involved in the King’s plot and sees it’s gone badly wrong. Horatio’s concern for Hamlet (rather than Laertes) makes his allegiance clear also.

In their 1916 edition of Hamlet, editors F. A. Purcell and L. M. Somers argue that:

From the dying words of Laertes we may infer that Osric was a party to the final treachery against Hamlet….he receives [the confession] without betraying any mark of astonishment.

Shakespeare, William. Hamlet. Eds. F. A. Purcell and L. M. Somers. Chicago: Scott, Foresman and Co., 1916. Shakespeare Online. 2 Aug. 2013.

Compare “the pass and fell incensed points / Of mighty opposites” above. Another subtle link between the two “duels” (one literal, one metaphorical) of this final scene: between Hamlet/Laertes and Hamlet/Claudius.

Laertes seems to signal that he intends to kill Hamlet on the next play (as opposed to letting Hamlet score?).

Is Claudius maintaining the fiction that he’s rooting against Laertes? Reconsidering or trying to abort the plan now that Gertrude’s doomed?

Claudius calls Hamlet “my son” in public in 1.2; “your son” in private with Gertrude here and in 4.5, and finally “our son” in 5.2.

Claudius calls Hamlet “my son” in public in 1.2; “your son” in private with Gertrude in 4.1 and 4.5, and finally “our son” here.

temper’d: mixed.

The play comes full circle and justice is done as the man who poisoned Hamlet’s father dies by his own poison.

If he used the same “distilment” he used on King Hamlet, the effects are going to look pretty ugly.

Hamlet finally, publicly unleashes some of the curses he’s been privately spewing against Claudius. He also echoes the Ghost in 1.5:

Ay, that incestuous, that adulterous beast…

Dane echoes the sense in which he used the term in 5.1–“This is I, Hamlet the Dane!”–in other words, the representative of Denmark, the King.