Noisms just put up a thought-provoking post about “consequences” in the dungeon. Not the social consequences of PC actions within the fictional world, though (although that would be an excellent topic to explore in depth, if you’re up for a certain kind of group-storytelling experience). The discussion is in terms of how the dungeon detects and reacts to the party’s presence.
He mentions three categories: light, noise and “combat.” This is where things get a little murky to me. “Light” and “noise” are almost self-explanatory. Most PC parties are going to need a light source underground, and will be less than completely soundless in their actions, and so the light and noise they produce will give sensory clues about their presence and actions to whatever else is down there with them in the dark. Simple enough.
But how does “combat” parallel with these? Noisms mentions several olfactory signs of battle: blood, bile, and sweat (“fear”), which suggests a parallel with the other two categories. But if a parallel were intended, why not just say “scent”? Why limit it to the aftereffects of battle? For that matter, there’s also mention of physical detritus and blood trails, which are more visual than olfactory in nature. The non-parallel nature of the three categories bothers me, so here’s an alternative breakdown.
Parties of PCs bashing through the dungeon give away their presence and activities in two ways: through their emanations, and through their leavings. Each of these can be further specified as triggering one or more of the five major fantasy sensory facilities: visual, audio, chemical, tactile, and supernatural.
Emanations are the signs of a being’s presence that it gives off just by, well, being present, and doing things. Noism’s light and noise are both emanations. The smell of a group of unwashed people who’ve been wearing armor all day, or the smoke of their torches, are emanations. The swaying of a rope bridge as they cross it is an emanation. The heat, noise, and magical tensing and release that accompany a fireball spell being unleashed in combat are all emanations.
Leavings are anything left behind to show that someone was there. The dropped weapons, broken arrows, blood and bodies, and so on that Noisms bundles under “combat” are all leavings. But so are spent torch stubs and other trash, footprints in soft ground, lingering scents or even lingering heat, ropes and pitons that remain after the party scales a sheer wall, remains of camp-fires and crumbs from meals, even the soft tingle left behind by the passage of a wizard or magical item, or the assembly of astral spirits that clustered around a cleric praying for magical aid.
There’s no harm in keeping things simple: just pick one major sense for any given dungeon inhabitant, and keep in mind that not everything will charge in to confront the party as soon as it becomes aware of them, or even necessarily care about their presence at all. Maybe a scavenging beast will come across the remains of a battle, do its scavenging, and move on. Maybe it will follow the PCs if it encounters their trail again but try to stay out of sight, having learned that they leave lots of food in their wake. They may never know… until they day when they need to retreat from an encounter gone bad, and there’s their private clean-up crew, waiting just around the corner.
In short: if you know that something is there (and something’s always there, somewhere), think about what senses it has. If the PCs are nearby, think about what emanations those senses would pick up; if they’ve come and gone, think about what part of their leavings it might notice. Then think about what it would do with the information. Then use that to make the PCs’ day more dangerous (not necessarily by attacking; any unknown is a potential threat and should be treated with caution)… and correspondingly more interesting.