Brontë described the ambiguity in the ending as a "little puzzle".

And I must admit, this does solve a little puzzle for me.

If you're going to look into this little puzzle, the place for you is the Kirk Building, where the matter originated.

The writers used the episode to solve several little puzzles, such as where Lisa's intelligence came from.

He lived for his little mental puzzles, and nothing else, exactly as he had told the prefect.

"Believe it or not, the answer to your little puzzle."

I mean, it's a perfect little puzzle for everyone to think about.

That had set him off on a little puzzle.

She smiled agreement, and he felt pleased with himself for solving the little puzzle.

It's an interesting little puzzle when you think about it like that.