How does Gertrude explain the death of Polonius?
Here's what she says:
Mad as the sea and wind when both contend
Which is the mightier. In his lawless fit,
Behind the arras hearing something stir,
Whips out his rapier, cries 'A rat, a rat!'
And in this brainish apprehension kills
The unseen good old man.
...Where is he gone?
To draw apart the body he hath kill'd;
O'er whom his very madness, like some ore
Among a mineral of metals base,
Shows itself pure. He weeps for what is done.
Her explanation for the killing is that Hamlet is mad, completely and hopelessly nuts. What she conveniently leaves out is his very telling line about the eavesdropping Polonius "Thou wretched, rash, intruding fool, farewell! I took thee for thy better." That "better" is obviously his uncle Scar, oops, Claudius.
She also leaves out all the things Hamlet said about her and her new husband the King and what a cold-blooded, incestuous, gross murderer he is. Nor does she mention Hamlet's little conversation with the Ghost of his father. She does add, out of nowhere, that Hamlet is remorseful about the deed ("He weeps for what is done"), which he is clearly not.
Could it be that Gertrude now knows that her son is anything but mad, that he makes a lot of sense, and she is finally behind him? Certainly looks that way.