From Dungeons and Dragons: Monster Manual I, the Green Slime was an underground hazard, that made misery of heroes venturing underground for treasure. It was the D&D version of toxic waste, just not as healthy.
“Green slime will attach itself to living flesh … [turning] the creature into green slime …”
We catalog another “underground hazard” from the realms of Dungeons and Dragons. It wasn’t enough to encounter traps or terrifying monsters in the dark. Monster Manual I documented many environmental dangers. The Green Slime was quite unfair as it ate through metal, wood and flesh. Only stone seemed impervious.
I regarded the slime as a thematic addition. A living trap that drops upon sound and vibration. It’s meant as an ominous warning. Underground is an unpleasant place.
Trivia: Cleaning up Green Slime is worth 610 XP. Sometimes, they are found in colonies of dozens.