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Ah.

The white stuff was scraped from the trench.

Notice that the last time in the trench animation is 7:26 and the first time in the scoop montage in reply 449 is 7:46.

Also notice that the white stuff at 6:33 not scraped is still white at 7:26.

Also also note the numerous "glints" in the trench.

I wonder what the plan is for this stuff? It looks to be "just" surface frost - not icy soil. Were they deliberately trying to get a sample of frost??