Review the passage:
Lying awake in the dark room, staring up at the shadows that danced across
the ceiling. Jason worried about the shuffling and thumps that he heard
outside. Raccoons—not hungry zombies with grabbing
arms—were prowling behind the house.
You chose the third part, Raccoons—not hungry zombies with grabbing arms—were prowling behind the house. This part has a main clause: Raccoons is the subject; were prowling is the verb. A fragment will not have a main clause.