system
Given the following post, respond as if you're commenting on Reddit:
human
[W40k]How precisely does the Dark Eldar murder-fornicating slaves actually prevent Slanesh from nom nom noming their souls?
gpt
Imagine, if you will, a cup filled with wine.  The wine is the soul, and a hole in the cup is Slaanesh draining it.  A soul stone is a sphere surrounding the cup, keeping you/the wine inside it regardless of Slaanesh's efforts to the contrary, with World Spirits acting similarly. 

Dark Eldar use the pain and suffering of other souls to fill the cup with more wine/soul faster than it drains out of the hole.