] "The Mousetrap" (I love that name for it) also shows us another problem with the general communication at Elsinore. Shouldn't Claudius' reaction to the play expose his guilt to more than Hamlet and Horatio?

Well, I think an issue is this: We are privy to Hamlet's thoughts on the subject. So we know exactly what Hamlet is up to and what he is looking for when he watches Claudius. Perhaps all the rest of the folks there see Hamlet acting all excited and loony, while Claudius is acting very upset. But since they aren't aware of any crime, or looking for any signs of guilt, they do not see it.