The cave is one that makes you keel over because it's near to origin of the fiend. The soil is dead, rotten, disgusting, and makes you retch just sniffing the air.
That's my take on it at least. Has to give an end of the world vibe after all.
Wanted to stretch this scene out a bit further so that Mary and Sasune would duke it out, but I am already behind, so he just gets a slap in the wrist.