Yoma 65: Why Is the Cow Like the Goat?

Focusing on the details of many possible cases in a way that seems harried, and perhaps is a diversion from larger worries. Also, why do we pasture the goat that isn't used (when a second pair is needed), and let it die,rather than let it live? The rationale is a bit difficult... And the Gemara seems to struggle with the "waste" of the animal's life here too.