Oh, my offence is rank. It smells to Heaven.
It hath the primal eldest curse upon ’t,
A brother’s murder.

Claudius utters these lines at the beginning of a soliloquy in which he confesses to murdering his brother. At first Claudius does not explicitly state that he killed his brother. However, his reference to the “primal eldest curse” that has been laid on his “offence” alludes to Cain’s murder of his brother, Abel, as recounted in the Bible. By comparing himself to Cain, Claudius illustrates that he understands the severity of his sin, and he expresses his sense of his own moral corruption through images of decay and putrefaction: his sin is “rank” and sends the smell of rot all the way to heaven. Additionally, Claudius’s confession also gives the audience (and only the audience) confirmation that he did, in fact, kill his brother. Hamlet’s apparent descent into madness might otherwise suggest that the murder conspiracy exists solely in Hamlet’s head, but Claudius’s confession clears this ambiguity up—but not for any of the characters in the play, sadly enough.

My words fly up; my thoughts remain below.
Words without thoughts never to heaven go.

These words come at the end of the scene after Hamlet, who enters with a sword intending to kill Claudius, decides not to murder his uncle while he’s praying and exits. In the lines quoted, Claudius echoes the debate he had with himself earlier in the scene concerning the effectiveness of his prayer. Specifically, he wants to know if he can be forgiven for his crime yet still benefit from it: “May one be pardoned and retain th’ offense?” By the end of the scene, Claudius remains in doubt, and the words quoted here demonstrate the extent to which he does not trust his own feelings. He wants to repent of his murder, but he doesn’t believe he really means it. In this sense, Claudius shares Hamlet’s penchant for self-doubt and indecision. Like Hamlet, Claudius fears that his words are ultimately meaningless.

Laertes, was your father dear to you?
Or are you like the painting of a sorrow,
A face without a heart?

Claudius asks these questions of Laertes after the young man returns from Paris on news of his father’s death. Claudius wonders whether Laertes actually feels as much grief as his performance of sorrow suggests. Claudius’s questions echo Hamlet’s earlier doubts about the grief of his own mother, Gertrude, and in this sense Claudius’s questions speak to the play’s larger anxiety about the mismatch between appearance and reality. Yet this quote also works on another level, establishing a contrast between Laertes and Hamlet. Laertes responds with deep offense to Claudius’s suggestion that he’s faked his grief, and he expresses an earnest drive for revenge. Unlike Hamlet, who keeps his rage largely to himself and trips himself up with uncertainty and hesitation, Laertes speaks plainly, telling Claudius he would cut the throat of the man who killed his father.