Passage Summary: Horses love grass, but their numbers plummeted right when the world started warming up after a long cold snap.

Reasoning: Horses do well in grasslands, yet their population crashed when the climate shifted from a cold period to a warming period.

Analysis: The mystery here is why a warming period would lead to a decline in a population that thrives in grasslands. Usually, warming is associated with increased plant growth, which should theoretically help horses. To resolve this paradox, we need a reason why this specific warming period was actually bad for grass or horses. Look for an answer that explains how the climate shift changed the landscape—perhaps by turning those open grasslands into forests that horses couldn't live in.