A written entry in my Hamlet notebook. See pithy remarks for my personal comments.
Act 3, Scene 2
The play begins with a dumb summary, an overview of the upcoming play without sound. The audience clearly witnesses the [Player Pois’ner] kill the [Player King]. However, Claudius displays no outstanding reaction, according to the text, making it questionable if he really felt guilty and left when the murder is acted out in detail. The dumb show may be at fault (it was at Hamlet’s direction), because Ophelia seems puzzled by it: “What means this, my lord?”(128).
'A poisons him i' th' garden for's estate. His name's Gonzago. The story is extant, and writ in choice Italian. You shall see anon how the murderer gets the love of Gonzago's wife. (246-249)
At this point, Hamlet appears to comment on the play as if he had already seen it. Right after, the King arises and leaves. If Hamlet had not made his little remark regarding the murderer getting the love of Gonzago’s wife, would the King have understood what Hamlet was trying to show? Then again, without further textual evidence, it is possible that Claudius reacted to something else; perhaps he just needed to go to the bathroom. However, to Hamlet and Horatio, it is evidence that Claudius had murdered King Hamlet and is feeling the guilt evoked by the play.