In science, a catalyst would be a substance that increases the rate of a chemical reaction; however, the definition when discussing language would be "someone or something spurring an event or action".
Peripeteia is my guess answer bu I cannot say I am right
The appearance of Akaky as a ghost at the end of the story is a product of ... A central theme or purpose of Gogol's short story is to expose people's lack of compassion. ... The techniques of humor and satire would help you address the topic.