Passage Summary: Scratches always appear on tools used to cut grain; since tools at one site weren't scratched, they must not have been used for grain.

Conclusion: The sickles at the second site were not used to harvest grain.

Reasoning: Grain harvesting always causes scratches on sickle blades, and the blades at the second site lacked these scratches.

Analysis: The argument assumes that if grain was harvested, the evidence of that use would still be visible today. To weaken this, we need a reason why a sickle could have been used for grain but still lack scratches now. Perhaps the scratches were polished off, or the blades were replaced, or the soil conditions at the second site somehow filled in the scratches over time. Look for an alternative explanation for why those specific blades appear smooth.