Please Post the story So I can answer your question and put who character S is.
It's a nonessential word, clause, or sentence added to an already grammatically complete sentence. It's most commonly set off by brackets, but it can also be set off by commas or dashes.
Example:
My mother went to the supermarket and picked up some strawberries (my favorite fruit) earlier today.
I believe the answer is ... an unreliable narrator
Answer
The mechanical hound was no in the cage
Explanation:
When Montag goes to the firehouse the mechanical hound is gone.
