Dust hangs heavy. Water drips. You push open a swollen door and BATS explode out - all of them, squeaking and flying, surrounding you in chaos. Standard jump scare. Except you've just triggered the dungeon's alarm system. Bats are creatures of thresholds, the gateway between civilized world and unknown. When they react to intrusion, they send a signal through the entire dungeon: something is here. By the time your players see the Swarm, monsters are already alert. Traps are already armed. The Owlbear nesting below knows. The Skeletons know. The dungeon that was silent for centuries has felt your arrival like a nerve firing. You thought you were discovering the dungeon. The dungeon was discovering you - and reacting accordingly.