By this point in Shakespeare's Hamlet, Claudius is becoming increasingly concerned about Hamlet's erratic behavior and with good reason. Hamlet never liked Claudius. Compared to his father, Claudius was "Hyperion to a satyr" and "no more like my father Than I to Hercules" (1.2.143, 155–156). Claudius married Hamlet's mother far too soon after Hamlet's father's death, and Hamlet has shown his displeasure with Claudius for that:
CLAUDIUS: . . . But now, my cousin Hamlet, and my son,—
HAMLET: A little more than kin, and less than kind!
CLAUDIUS: How is it that the clouds still hang on you?
HAMLET: Not so, my lord: I am too much i' the sun. (1.2.64–69)
Then Hamlet starts acting a little crazy. Claudius isn't sure if it's all an act, but he needs to be careful, so he tells Rosencrantz and Guildenstern to spy on Hamlet:
CLAUDIUS: Something have you heard
Of Hamlet's transformation
. . . What it should be,
More than his father's death, that thus hath put him
So much from the understanding of himself,
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