GM:
You climb up and on your way you find a passage that the spider climbed out of, which is a man made tunnel that terminates at the well with a railing stone railing. It is too dark to see down the tunnel.
So, the way I envisioned this was that the railing is more like a half wall, but let's, but I said railing (in fact, I said it twice, lol), so let's go with that. Saran kicks the rat through the railing and lands with a thud down the dark well with the dead spider.
The curtain is mostly burned away at this point. The webs that Saran had cut away caught fire too and there are a few burning embers on all faces of the mouth of the tunnel where cave moss, lichen, and fine roots were burned.
From the room inside you hear a furious fluttering and just at the reach of your vision, you see a swarm of bats upset by the smoke barreling toward your tunnel.