Is very simple, although the term "chaser" may not be as commonly used as it was when John Collier wrote his story. A chaser is a drink that is taken to follow the first alcoholic drink.
Answer:
The complete subject would be SpongeBob SquarePants's best party trick.
Explanation:
The subject, or thing completing the action, is SpongeBob SquarePants. But the complete subject would be his best party trick because it gets into one of his distinct attributes.