Help, I've been killed!

I have seen Hamlet performed twice, but have not noticed this particular line and how it worked for the actors. Bizarrely, in Act 3 scene 4 page 111, after Hamlet discovers a man, Polonius, is hiding behind the tapestry and listening in to his conversation with his mother, he draws his sword and says, "How now! A rat? Dead, for a ducat, dead!" Stage directions say, "he kills Polonius with a pass through the arras." Then, surprisingly, Polonius exclaims, "O, I am slain!"

Not only am I confused on the possibility of someone exclaiming, "O, I'm dead," I also know that would be a tricky scene to accomplish on stage. After all, it real life when we are fatally struck through with a sword ... those would not be the words that would come to mind.