Chen Zhou saw that the snow near the entrance of the cave had all been cleared away, especially the area closest to the snow-blocking canopy, where clear marks from branches were left on the ground.
The wind blew all day long; in no time, shallows and grooves on the ground would get covered up by snow blown in. If the marks were still visible, it meant that someone inside had recently been working outside.
Apart from the relatively clean ground, even the chimney extending from the snow-blocking canopy had been cleaned.
Warm smoke, blowing from inside to outside, melts the snow. Once melted, the snow on the chimney trickles down and freezes. Over time, it forms huge chunks of ice, not just easy to trip over, but also blocking the chimney, preventing the smoke from escaping.
