Final answer:
The event from the excerpt of Shelley's 'The Cenci' symbolizes the falling action stage in Freytag's Pyramid, where the aftermath of the climax is being addressed, advancing towards the story's resolution.
Step-by-step explanation:
The excerpt from Percy Bysshe Shelley's The Cenci depicts a moment of significant change following the murder of a character, indicated by Beatrice's perception that 'Darkness and Hell have swallowed up the vapour they sent forth'. This event can be associated with Freytag's Pyramid and represents the falling action stage. In Freytag's model, the falling action follows the climax, which is the point of highest tension or the turning point of the story, and precedes the resolution. The falling action is where the consequences of the climax unfold, and in this case, it is where the characters deal with the aftermath of the murder, leading towards the finale of the narrative.