During last session, the players heard a rumor about Living Pits (DFM3) being just one of many living "things."
"Living stairs!" said Hamilcar's player.
What else makes good living, threatening dungeon features?
Living ceilings are just lurker aboves, and floors are trappers.
Living elevator rooms?
Living 5 degree slopes? Perhaps the slope just moves around, slanting the dungeon.
Living dungeon decor is all-too-common - statues, hostile furniture, gargoyles - but living features, I don't know. Did I miss any?