Passage Summary: Mr. Xu thinks squirrels have a secret 'anti-freeze' in their blood to survive the cold, but Ms. Yerky says that's not true because in a lab, their blood freezes just like regular water.

Conclusion: The arctic squirrel's blood does not contain a special substance that prevents it from freezing.

Reasoning: Laboratory experiments show that vials of the squirrel's blood freeze at the exact same temperature as water.

Analysis: Ms. Yerky's method of reasoning is a direct empirical rebuttal. She takes the central premise of Mr. Xu's argument—that the blood has a lower freezing point due to a special substance—and provides experimental evidence that contradicts it. Note that she doesn't offer an alternative explanation for why the squirrel doesn't freeze in the wild; she simply focuses on debunking the specific mechanism Xu proposed.