Once the rumor that Hamlet killed Polonius spread, people would begin to wonder who to trust and disasters would begin to occur. A sword was very common and became more and more dangerous the more it was used to commit murder. I don't believe it's a coincidence that the "challenge with the sword" at the end of the play resulted in the deaths of Hamlet and Laertes. A poisoned sword by King Claudius killed them both. The sword also represented the irony that Hamlet was "trying" to kill Claudius with his own, but Hamlet ended up dying because of a sword that Claudius poisoned. This scene was successfully filmed thanks to Kenneth Branagh and his use of