1. Ophelia rejects Hamlet - this is the part where Hamlet grows angry and tells her he never loved her, and that she should become a nun because women don't deserve much more
2. the play within a play - Hamlet had the actors enact the events from his real life so as to see whether Claudius will reveal his guilt
3. Claudius' attempted prayer - he understands that what he did was wrong and he regrets it, however, it is too late for him to go back now
4. Polonius killed - Polonius was hiding behind a curtain, and Hamlet thought it was Claudius, and thus killed him