Sentence:  Not only does Sturgeon break the “<WSD>fifth wall</WSD>” between playwright and audience in section 7 of this story (becoming a sort of character in the story himself), he goes further in section 8, breaking a sixth wall by warning the reader that he or she may already have become infected by the parasite just by reading this far. 
Meaning of the word marked with <WSD> tags:  The divide between critics or audience members and author or theater practitioner.