Surprisingly for a production that features a lot of mirrors (in the hall, but at least two in the Queen's closet), Branagh does not use them on the "set you up a glass" line, completing an image from the Nunnery Scene and linking Ophelia's potential whoredom with Gertrude's proven one (all in Hamlet's mind, of course). The scene doesn't suffer as a result, however, since the line itself does some of the work. The backdrop surrounding the room is of particular interest, a painting of people and the occasional dog sitting on steps and balconies, like a makeshift audience. This is judgment day for the Queen, and all of Denmark metaphorically looks on, trying to force shame on her. The scene begins with some energy, as Polonius rushes in and Gertrude, ever impatient with him, pushes him behind a curtain. Hamlet's own entrance rides that momentum, motivated as he is by a mixture of elation from the success of his play, and anger at not having been able too kill Claudius. He goes for the Queen's throat, and she naturally cries "murder", though one might imagine he was merely looking for some locket with the King's picture in it... except that while other productions use such a prop, this one has bigger bedside framed pictures.
The accidental murder of Polonius is well-choreographed, as he falls wrapped in the thick curtain, keeping his identity hidden from Hamlet for the time it takes the prince to inquire if it's the King. Polonius' highly redundant "I am slain" is retained, making the character's last words completely unnecessary verbiage, the perfect epitaph for the character. Branagh makes it clear this changes Hamlet as a person, though it may take a few moments to truly sink in. He is now a murderer, the same sin he holds against Claudius, and worse, he has killed a father. His voice breaks when he gives Polonius his farewell, and he drops the dagger in disgust. He gets back on track as soon as he sees his mother wringing her hands, however, as if she has no right to this shock when her own hands are stained with his own father's blood.
He throws her on the bed where much of the scene takes place, but thankfully, Branagh does not go down the Freudian route, at least not explicitly. He lets the words do the work of presenting a sexually immature Hamlet who, like a child in this part of the scene, is repulsed by the idea of his parents having sex. If the audience wants to read an Oedipal complex in the inappropriate way he talks about his mother's sexuality, they are free to do so, but the idea is not expressed in the staging. Violence and impertinence, yes, but the characters are not sexually inappropriate with one another. As the scene progresses, the life is sucked out of Gertrude by her son's revelations and/or reproaches. Shame or tiredness? Her expressions are ambiguous. It is perhaps important that Gertrude looks only at her former husband's picture and not Claudius', but again, it is ambiguous whether the memories evoked are good or bad, and whether she's evaluating the brothers against Hamlet's praise and slander.
The Ghost reappears, this time as a veritable "king of shreds and patches", kinder and sadder than his angry, armored self. The Queen's point-of-view omits him, leaving the audience to wonder if he is real and in control of who can see him, or if is he completely imaginary and as the Queen fears, an artifact of Hamlet's madness. Hamlet is, in fact, desperate for his mother to also see the Ghost, actively questioning his own sanity when she does not. The speech that follows about his sanity is in that sense as much for himself as it is for her. The Ghost, potentially a devil in the earlier scene, has a very different attitude, obviously tempered by his obvious love of Gertrude and his wish that no harm come to her. It's almost as if he regrets the fury with which he gave his earlier command, and wishes not only to sharpen his son's "blunted purpose", but to make up for the consequences his dread command incurred. It's all gone off the rails, as they say, and it's ultimately his fault. If Hamlet was impetuous before, in front of his father he is truly a child, and he cries like one.
Once the Ghost has left, he attempts to prove his sanity, a difficult feat given that he starts by pushing his mother onto a bench after she's seen him hallucinate. But this visitation, and the blood now on his hands, have changed him, even possibly awoken him from madness. He'll be far more in control of his words and actions from here on out. Moving away from the childish outrage of mere moments ago, he takes on a paternal attitude towards Gertrude, instructing her calmly on what to do about her situation. The fact that he's now a sinner too has leveled the playing field. He asks her to repent, but repents his own actions as well, as an equal partner should. He's gone too far and knows it, and if his assumed madness became real, he now reigns it in, turning it back into craft. As Hamlet takes responsibility for what he's done and for what he must do, he becomes a darker, even more fatalistic Hamlet. The resigned way he takes care of Polonius' body, calling it "guts" (previous speeches have been concerned with the state of the soul after death, but from here on out, the dead are decaying objects), is proof of that.
The final image of the scene, with a reflective puddle of blood dominating the foreground as Gertrude paces anxiously and tries to make a decision about who to trust, is symbolic of her part in Hamlet Sr.'s murder (she was its inspiration) AND of her son's madness which caused Polonius' death. She is torn between the two, and given how under-written Gertrude is, it will take some time to clear up just which side she takes.
