Beatrice. I just really don't know what to think anymore.
Fine Giovanni. I will drink from the phial.
Before Giovanni goes to give the phial to Beatrice, he looks into the mirror and sees a spider. He moves closer to it, and the spider drops dead. His breath killed it. He is contaminated with poison from the garden. This scene shows us the climax of the story because Giovanni has now been contaminated of poison.
In the garden Giovanni questions Beatrice. To prove her innocence she drinks from the phial. In this scene we see the resolution of the story.
In result, Rappaccini watches in horror as she dies in front of him.