Final answer:
Hamlet mistakenly kills Polonius, thinking he might be stabbing King Claudius, who he believes is behind the curtain eavesdropping.
Step-by-step explanation:
When Hamlet hears Polonius's voice behind the curtain, he reacts impulsively, believing it might be his uncle, King Claudius, who is eavesdropping. In a fit of rage sparked by this belief, Hamlet stabs through the curtain, unintentionally killing Polonius. This act of violence helps to drive the narrative of the play forward, leading to further tragedy and the escalation of conflict among the characters.