Why does claudius put a pearl in the cup?

King Claudius in act 5 scene 2 of Hamlet puts the pearl in the cup to ensure Hamlet’s death. The pearl is a backup plan just in case his step-son, Hamlet survives the supposedly friendly duel with Laertes. Having accidentally killed Polonius, Laertes’ father, Laertes is using the sword fight to seek revenge urged on by King Claudius. Towards this end, the king arms Laertes with a poisoned sword. On the other hand, he encourages Hamlet that he will win the duel even putting a pearl in his stepson’s wine cup to toast his imminent victory. The gesture is meant to give the impression that the pearl is a reward. Claudius’s actions are fueled by fear that Hamlet will discover that the King killed his father who was also the king’s brother. As a precaution, the pearl is poisoned to make Hamlet’s death definitive. Oblivious of the plot against his son, Gertrude who is also the king’s wife reaches to drink to Hamlet’s impending triumph. Claudius dissuades her but does not insist enough leading to Gertrude proceeding to drink and die.  

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