How does the author use foreshadowing in Uncle Vanya?

Act Three is the climax of the play, and Vanya's emotional outburst, in addition to his attempt to kill the Professor serve as a release of his anger and resentment. In his violent explosion, Vanya, unlike the rest of the characters, finally does something. The irony, of course, is that both his shots miss the Professor, making Vanya's life even more useless, at least in his own mind.

Before that moment, however, we have three quieter explosions that are in some ways even more powerful. In the first, Sonya says that she can't take not knowing what Astrov's true feelings are any longer, and asks Yelena to help her find out the truth. This is both ironic and sad, and for the same reason. Yelena knows, and we also know, that the reason Astrov visits every day is that he's attracted to her. Yelena also knows that at some point Sonya will find out the truth and will be hurt. This little explosion foreshadows Vanya's bigger explosion, with both explosions answering the question posed by the play's theme: if you live a life of emptiness long enough, you may end up in a place where you'll take desperate measures to fill that emptiness.