Area 21. The Agitated Chamber
This room is another example of why I think the Tomb of Horrors is just too clever by half. The gimmick here is just overly complicated, and like every other area, is presented in a great, long wall of text.
"specially anti-magic treated creations of green slime and brown mold."
If the PCs tear the tapestries, the tapestries turn to green slime. If they burn the tapestries, the tapestries turn to brown mold. If the PCs don't intentionally tear or burn the tapestries, the vibrating floor gimmick will probably force a tear. It's like the designer was just trying so hard to make this a deadly room that things just got ridiculous.
I have no real idea how Gygax came up with the idea for this trap, but my imagination comes up with this:
Playtest 1: PCs walk in, tear away tapestries to search the walls.
Edit 1: DM makes tapestries turn to green slime if torn.
Playtest 2: PCs don't tear down tapestries, choosing, instead to burn them away.
Edit 2: DM makes tapestries turn to brown mold if burned.
Playtest 3: PCs don't destroy the tapestries, choosing, instead, to just move them aside.
Edit 3: DM adds the bouncing floor to force an accidental tearing of the tapestries.
Playtest 4: PCs use 10' poles to cautiously and carefully move tapestries.
The DM is satisfied that the PCs are sufficiently paranoid and scared of the room.
Considering how easy it should be for the PCs to just slide the tapestries out of the way to search the walls, it seems that this trap will only catch PCs who are intentionally destructive in their searches.
Bullgrit