Learning from Nature: the Mechanics of Traps

A fascinating article in the Atlantic describes the mechanism of the Venus flytrap as scientists have studied it. It's a great description of the Venus flytrap's mechanics, which through evolution shows how an unthinking plant can hijack the instinctive survival response of an animal. Its process is instructive in how we can think about trap design.

First, the trap is appealing. A fly comes along because it smells something sweet. By making itself attractive the flytrap uses the appearance of other plants around it as an offensive weapon. Since the fly can't tell immediately that it's a trap, it comes in to inspect. Only then is it doomed. This is a good principle for elaborate traps in D&D. PCs are always looking for treasure. Appearing to present a treasure is a good way to present a trap, but not the ideal way.

D&D players aren't, no matter what some referees may tell you, as dumb as flies. A trap that's simply too obvious, such as a chest of shimmering jewels and gold coins unguarded in the middle of a room, will be regarded with the utmost paranoia. It's obviously a trap. A really great baited trap is one that looks like hidden treasure. It's hidden in a secret compartment or panel that can be found by careful PCs. Such a subversion is cruel, but sometimes the best way to spring a trap on players is to make them work for it.

Second, the trap has error-checking. It only closes when two of its cilia are brushed. This is a wonderful principle for mechanical traps: the trap is not triggered on the first pass. The primary reason for this is to avoid false alarms, as described in the article. This is good and pragmatic. But with a D&D style trap, there is a further benefit where the party is drawn deeper into the trap before it springs. A simple pit or arrow trap will kill only one member of a party, but it is reasonable for trap designer to aim for multiple kills. And it may also be a way for monsters (or clever PCs) to avoid a trap by letting it reset after the first trigger.

There are two good ways to implement this principle with a D&D trap. One is to require a single trigger to be pressed more than once, such as a pressure plate that activates a two-step process. The first step cocks the arrow and the second fires it. The other is to have two separate triggers, one that starts the trap process and a second that finishes it. Either can work and both are nasty surprises.

Third, the trap imprisons without killing. This can be useful in a faction dungeon where the monsters might prefer to question a member of a rival group spying on their territory rather than killing them. The victims of such a trap become useful bait or can be traded in a prisoner exchange. This can lead to a tense period where the PCs have an opportunity to try to escape before the monsters who set the trap come to check it. Or the designer may have abandoned it and the trapped characters are stuck until a wandering monster comes along.

A trap that doesn't kill outright is extra fun if it affects only a single PC. The rest of the group simply sees the lead PC go missing and isn't sure exactly where they are, while the trapped character has to deal with their predicament on their own. It presents the immediate dilemma of how much effort to spend on saving the trapped character. And as noted about the factions above, such a PC may be a bargaining chip that stops the rest of the characters from barging in and killing a monster group.

Fourth and most brutal, the trap makes its victim kill itself. The fly's struggles against its captivity doom it. Standing still would be the best policy, but it goes against their instincts. This can be copied in straightforward ways, such as by having the character trapped so tight that they can't struggle to get out without impaling themselves on a spike, or puncturing a container of poison gas or acid. It could also be a question of physics, if the trap is suspended more than 10' above the ground. Even a simple quicksand type of trap, where struggling to extract yourself actually pulls you in further, does a great job with this principle.

But this can be used in more devious and subtle ways. Efforts to escape can let the players, who again are still smarter than flies, outthink themselves. Elements of the trap itself may be unstable or unsafe, or designed in a misleading way. What looks like it will open a door actually operates a hidden ballista, or opens a chamber above full of heavy rocks. You can go way too far in this direction and wind up in Grimtooth's Traps, but I think there's a lot of fun trap design short of that.

I love the concept of the Venus Flytrap. It's an elegant and simple life form, and does its work without even the simplistic thought patterns of the fly, but it does something very intricate and involved. Its principles can lend a lot to any trap in your dungeon, whether you pick one or all four.

Oh, and don't forget the simplest way to apply lessons from this article in your dungeon: giant Venus Flytraps.

Carnivorous Plants and the Dungeon

Reading about exotic South American mountains and their unique flora got me thinking about pitcher plants, which are also known as pitfall traps. These tend to be small, exotic plants that trap insects and convert them into nutrients. The pitchers of plants like Nepenthes lowii, pictured to the left, tend only to run as long as 35 centimeters (just over a foot). But this is Dungeons & Dragons; if there is one thing the game is good at, it's taking things and making them bigger.

You probably already know where I'm going with this. Sticking a pitcher plant, particularly one with a snap-shut "lid" like Nepenthes lowii, in a D&D pit trap is a wonderfully nasty surprise. The hapless dungeon delver falls in, and all of a sudden they're trapped in a suffocating plant, trying to get some weapon free and cut their way out while they still have air left. Meanwhile the digestive liquid burns them as it starts to turn them into plant food. Their friends can to try and cut them out, but that's pretty dangerous.

The tentacle of the sundew Drosera capensis is another nasty trap. When the long hairs are sprung, the sticky tentacle curls up and rolls its prey into more of its digestive juices. This one might, depending on size, do crushing as well as acidic damage as it entraps a character. These liquids should, by the by, also be doing a number on armor even if the PC gets away; a coat of mail or plate that is scarred and pitted by acid is no longer useful for defense. These can be in pit traps as well, or used as room traps in a weird sort of "garden room."

It should be obvious why carnivorous plants are the kind that thrive in a dungeon, of course: lacking much in the way of sunlight, dungeon plants will consume flesh. And it lets you have plants in your underworld in a semi-logical way.

Of course, we can hardly discuss carnivorous plants without talking about the Venus flytrap. Once the trigger hairs on this plant are sprung, its powerful leaves snap shut and the unfortunate insect caught inside is done for. A huge flytrap can catch a single character, but a really massive one could even get a whole party. Again we're relying on the combination of crushing damage and acid to actually do in the character. The initial blow as the flytrap shuts might also do some damage. They're iconic and, like the pitcher plant, will pose the difficulty of freeing a trapped character without harming them. Dungeon variants might have hardened bristles that do damage while the flytrap closes.

Plants, of course, are typically something we see only above ground. This makes their appearance in the dungeon setting startling, and clearly the sign of weird Chaotic mutation and/or a mad wizard's experimentation. Of course, you could always go full-on Little Shop of Horrors or Attack of the Killer Tomatoes as the end stage of dungeon carnivorous plants; but I think the initial horror of being consumed by a pitcher plant in a pit trap or caught by a giant sundew is a great way to incorporate some plant life into your dungeon crawls.

Sundew image by Noah Elhardt CC-BY-SA
Venus flytrap image by Noah Elhardt CC-BY-SA

Mud and Gas: Taking Inspiration from World War I

Far more treacherous than the visible surface defences with which we were familiar, such as barbed wire; deep devouring mud spread deadly traps in all directions. We splashed and slithered, and dragged our feet from the pull of an invisible enemy determined to suck us into its depths. Every few steps someone would slide and stumble and, weighed down by rifle and equipment, rapidly sink into the squelching mess. Those nearest grabbed his arms, struggled against being themselves engulfed and, if humanly possible, dragged him out. When helpers floundered in as well and doubled the task, it became hopeless. All the straining efforts failed and the swamp swallowed its screaming victims, and we had to be ordered to plod on dejectedly and fight this relentless enemy as stubbornly as we did those we could see.

Private Norman Cliff, 1st Grenadier Guards, To Hell and Back with the Guards, quoted in Peter Hart, The Great War: A Combat History of the First World War.

Dan Carlin furnished this reference in his fine podcast, Hardcore History, talking about World War I. And it strikes me to the bone; in the last six months or so I've developed a strong interest in the first World War and its attendant horrors, in no small part because it was so bloody and total a war, but unlike World War II, most of the atrocity was on the battlefields and not being perpetrated upon civilians.

The Third Battle of Ypres, also known as Passchendaele, stood out for one reason: the mud. Norman Cliff's description above does it far more justice than I can, but it was just pervasive and awful, and it was total. Soldiers had to live with it for months. It was a carrier of filth and disease and unlimited horror. People shat in it, people died in it, shells exploded in it, and you had to live with it. Wooden planks made easy targets for artillery and machine guns.

Mud is a hazard that is totally natural for RPGs. Outdoor locations are extremely liable to be mud-spattered in rainy seasons, while underground locations with an earthen floor could, under sufficient flooding, turn into a quagmire not unlike those in Passchendaele. Particularly nasty is when the characters are caught in a torrential downpour and the area around them changes from fields into a swamp. The mud in Ypres was compared to the consistency of cheesecake, and soldiers would slowly sink in like quicksand.

Armor is absolutely a disadvantage in these situations. A World War I soldier's kit is fairly comparable in weight to a fully loaded fighter wearing plate armor; if a character in plate falls into sufficiently deep mud, they need to be pulled out or they will drown. Chain is less heavy and probably gives a better chance to get out, although the armor might be ruined by caked-on mud holding water close to spots that will then be rusted out.

It also feels appropriate for various horrors to be lurking within the mud. Even relatively shallow mud, where characters aren't at risk of drowning, can be made hazardous this way. Permanent mud might be home to nasty dire versions of worms or crayfish or other things that creep through the muck. And I'm always a sucker for scenes like the one in Star Wars where the mynock drags Luke down in the trash compactor.

And mud is a great place to hide pretty much anything. It could be treasure that was once buried, or a door half-hidden by muck where opening it is a logistical challenge, or a floor now covered that holds a secret message.

The first world war was also the first time that chemical warfare was widely used. The horror was brilliantly captured by Wilfred Owen in his well-known poem "Dulce et Decorum Est":

Gas! GAS! Quick, boys! — An ecstasy of fumbling,
Fitting the clumsy helmets just in time;
But someone still was yelling out and stumbling,
And flound'ring like a man in fire or lime ...
Dim, through the misty panes and thick green light,
As under a green sea, I saw him drowning.
In all my dreams, before my helpless sight,
He plunges at me, guttering, choking, drowning.

Mustard gas was another "gift" of the third Ypres, an irritant that first developed only red patches but would soon turn into excruciatingly painful blisters, often blinding the victim temporarily and then leaving him scarred for life, and often permanently blinded. In a certain sense, choking to death on phosgene or chlorine gas was fairly merciful.

Gas traps are a D&D commonality, but are often all-or-nothing affairs. The gas kills you, or puts you to sleep; there is none of the sheer horror that mustard gas put into British troops on the Ypres salient. Choking tear gas is often used on civilians in the modern world, but if your fantasy setting has sufficiently advanced alchemy, it could very well be a part of everyday life in the dungeon. Particularly striking would be opponents that have some sort of gas masks; the picture above of a German cavalry man wearing the Stahlhelm and gas mask as he carries a lance astride his horse is the kind of outlandish anachronism that the first world war created.

Of course, turnabout is fair play, and it is entirely possible for the PCs to use gas against the enemy. The Cloudkill spell is literally a gas attack, after all, but captured or invented chemical gas is also a potent weapon. At this point, of course, the biggest danger of chemical warfare must be remembered: one does not normally control the wind direction. In a dungeon this can be particularly nasty, as a lack of moving air could simply turn a gas bomb into a barrier that lingers for hours.

The first World War devastated a whole generation of men, some of whom (like Tolkien) turned out to be Appendix N authors. It dashed the dreams that science and modernity had only good things to offer, and created yearning for an idyllic past. At the same time, it formed landscapes on earth that would have previously only been thought of as godforsaken blasted planets, and blew away the pomp and glory of the 19th century in a storm of steel. When you need to create an atmosphere where humans are stretched to their breaking point, World War I is the logical place to turn.

Actual Play: Fun with Infravision and Alignment

Infravision in B/X is described explicitly as "heat-sensing sight." So I tend to play the sight of elves and dwarves as being very broad; only the ability to see vague shapes of heat, generally not making out anything of the details of a monster.

Which was fun with the first of two encounters my players had with velociraptors last night. The raptors showed up during the first watch of the evening, and had the players surrounded, but there were only three of the raptors. The party's elf and one of the clerics were on watch, so the raptors were considering them potential prey until the cleric shouted everyone awake. The raptors disappeared in a flash (I give them a very quick movement rate) and it seemed like a false alarm. At this point they still weren't really sure what the threat was, other than that it was three or four feet high but broad and very fast.

The PCs wound up going back to the ruined palace where they had previously slaughtered some toad-men. Some exploration got them to investigate the statue in the courtyard, which had certain stops in its direction where it pointed. Investigating one of them led to another encounter with the raptors, who were now defending their nests and not just being curious. I described their motion with some keys that echoed Jurassic Park. The players got out, with only the hobbit getting a scratch when he went to his backpack to try and get some meat to slow the raptors down.

Deciding to try their luck elsewhere in the ruins, the PCs checked out a small block of rooms. This time they found a corridor with some caltrops in it; had they gone in without being wary it would have been a bigger problem for them. Around the next corridor they did get hit by a crossbow trap, and while investigating it found that they had the interest of a big, menacing warrior type. The players' reaction to his weapon, a military pick that they later found out was aligned with Chaos.

Once they dispatched the warrior and his companions, they found more materials, including a letter written in Chaotic. This was translated for them by one of the Acolytes from the Caves of Chaos, who has been charmed by the elf and is being used as a makeshift henchman. It's been fun to sort of let the idea of "forces of Chaos" as a persistent, but not unified, threat; the way I interpret Chaos working in my world is that powerful Chaotic characters are in touch with patron deities, and each such leader is a sort of absolute tyrant who imposes their will on their underlings. So there is now someone in dungeons (not yet discovered by the PCs) under the ruin who has transgressed against the forces loyal to the Chaos god Arioch.

I was very happy to be able to play up the Chaos and dinosaur aspects of this ruin in one session. It's been interesting in terms of PC balance, too: although there are two fourth-level fighters, who can take a fair number of hits, the rest of the PCs were 1st or 2nd level this adventure. One of the clerics hit 3rd, as did the hobbit, which will make the rest of this particular adventure interesting.

Pit Trap Generator

It's become a thing to have generators on your blog. This is one for pit traps. Click the button below and it'll generate a fresh pit trap for the next time your PCs need something to fall into.

(This is based on my article from Fight On! 14.)

Of Tricks and Traps

The fear of "death", its risk each time, is one of the most stimulating parts of the game. It therefore behooves the campaign referee to include as many mystifying and dangerous areas as is consistant [sic] with a reasonable chance for survival (remembering that the monster population already threatens this survival). For example, there is no question that a player's character could easily be killed by falling into a pit thirty feet deep or into a shallow pit filled with poisoned spikes, and this is quite undesirable in most instances.
- The Underworld & Wilderness Adventure, p. 6.

The paragraph above is likely to have been written by the very same author who would later pen S1 Tomb of Horrors; what a difference a few years makes.

When you read the list that runs beneath this text, the tricks and traps are definitively different from the list in Appendix G of the Dungeon Masters Guide. It's mostly about confusing mappers and getting PCs lost in the dungeon rather than actually killing them; teleporters, illusions, deceptive corridors, stairs going up or down multiple levels, etc. Whereas by the time Gygax wrote the DMG, it was primarily traps that shoot, stab, burn, drop or poison hapless characters, possibly to their doom. None of this is listed in the OD&D ideas, although there is a pit trap in the sample map. It is not so much an elaboration as a shift in the basic workings of tricks and traps from map hazards to PC killers.

I don't think that it's entirely coincidental that the change occurred after Gygax had started to put out printed dungeons that are very different from his original Greyhawk megadungeon. The difference between Dungeon Geomorphs - which are close to what we've seen of the Greyhawk maps in style - and dungeons like G1, G2 and G3, or B2 and S1, is a shift from dungeons where mapping is a key difficulty to more "logical" (but still nonlinear) dungeons that TSR put out in its heyday. Traps reflected the fact that combat and hazards were more likely to involve PCs getting hurt or killed than lost.

My love for traps stems from the idea that D&D is basically a hidden map game. Both types of trap have the same basic premise: that navigation of the dungeon should be inherently unsafe. A dungeon is an area hostile to intruders; if it weren't, it would already be cleaned out. But the failure state of the "damage" trap is more quickly resolved than that of the "get lost" trap. In the latter case, the referee is opening up the door for a session of players just trying to find a way out. With a damage trap you either get hurt or you don't.

One of the big advantages of damage traps over get-lost traps is that it's easier to create ways to avoid damage traps. If an arrow trap is triggered by a tripwire, then simply not touching the tripwire leaves you safe, trap avoided. You can't really do that with a space distortion corridor (suggested in U&WA) designed to screw up mapping; the referee has just messed with your map but no idea why is given.

None of which is to say that get-lost traps have no place in the game. Dead end corridors, one of the original suggestions, are a great feature - particularly if a wandering encounter begins chasing the PCs at a good clip. One way doors are also interesting, because they force the PCs to find a different way out without getting into the whole, "Hey, you're lost and your existing map is FUBAR." And teleporters are just fun, although I prefer the kind that have to be actively touched - there are several great examples in Stonehell that lead to really interesting scenarios. But on the whole I think that get-lost traps should be used sparingly.

It seems logical to concentrate traps in front of valuable objects or key lairs, but I think this attitude can be mistaken. If traps always come right in front of the treasure, then players will catch on to the pattern. One trick I particularly like is having traps poised before a turn that leads to a dead-end. Intelligent dungeon denizens will only go down such corridors carefully, but they make a great fake-out moment in dungeon design. Logically what these traps are doing is to catch intruders who are unfamiliar with the local architecture.

One thing that OD&D really got right was the rule for triggering traps: "Traps are usually sprung by a roll of 1 or 2 when any character passes over or by them. Pits will open in the same manner." It's a great rule to follow as a referee; you casually roll the die as the PCs are walking; I recommend only rolling once so the flurry of die rolls don't give the game away. Since I casually roll dice frequently in my games it's not noteworthy. And then a session later, the passage that the characters had passed without incident now opens up and someone falls into a pit. It's a great twist, and helps reinforce the idea that the dungeon doesn't become safe with time. Curiously this works much better with the later damage traps than with the get-lost type of traps that OD&D had foregrounded.

I'll finish with this. Traps are a spice in the dungeon, and it's definitely possible to go too far with them. I think putting in a trap in 1/6 rooms (the rate you find in Moldvay's rules for dungeon stocking) is a bit much - also that I don't think many traps should be in rooms proper as opposed to corridors. But a dungeon without them is just bland.

As for tricks, I'll be doing a follow-up focusing on them.

S&W Bonus #2: Pit Traps!

Since everyone's having so much fun with S&W Appreciation Day, here are some charts to liven up your pit traps. Not terrifically S&W specific but hey, I like trap charts.

The tables below are intended to put some variety into the standard pit traps that one encounters from time to time in dungeons. Roll once on table 1 for the pit depth, once on table 2 for the dimensions, once on table 3 for what is covering the pit, and once on table 4 to determine any special features.

Table 1: Depth of Pit
01-10	5 feet (1d2 damage)
11-50	10 feet (1d6 damage)
51-65	15 feet (1d6 damage)
66-80	20 feet (2d6 damage)
81-90	25 feet (2d6 damage)
91-99	30 feet (3d6 damage)
00	Infinite (characters fall “forever”)

Table 2: Width and Length of Pit
01-10	2 feet by 2 feet (victims may become stuck)
11-30	5 feet by 5 feet
31-50	10 feet by 5 feet
51-80	10 feet by 10 feet
81-90	10 feet by 20 feet
91-00	10 feet by 30 feet

Table 3: Trap Covering
01-10	Open pit
11-30	Trap Door, Stays Open
31-40	Trap Door, Resets after 1d6 turns
41-50	Wood (only triggered if more than 200 lbs weight is above pit)
51-60	Glass (shatters if more than 100 lbs weight is above pit)
61-70	Loose stone (crumbles to reveal pit beneath)
71-80	Sliding section of stone (moves away; resets itself after 1d6 turns)
81-90	Cloth covering (canvas or other fabric; goes into the pit first)
91-95	Illusion of actual floor (can be disbelieved if pole or other object goes through)
96-00	Solid stone; magically disintegrated if more than 200 lbs above pit.

Table 4: Special Features
01-35	Bare Floor
36-45	Spikes, Wooden (add 1d4 damage)
46-65	Spikes, Metal (add 1d6 damage)
66-70	Spikes, Metal, Poisoned (add 1d6 damage + poison)
71-80	Animal (consult Table 5)
81-90	Carrion
91-00	Filled (consult Table 6)

Table 5: Animals in Trap
01-30	Rats, Normal (2-12)
30-50	Rats, Giant (1-6)
51-60	Lizards, Giant (1-2)
61-70	Beetles, Giant (2-8)
71-80	Insect Swarm (various)
81-85	Snakes, Cobra (1-4)
86-90	Snakes, Vipers (1-4)
91-95	Killer Bees (2-12)
96-00	Bear, Black (1)

Table 6: Filled Traps
01-50	Water, Normal (if deeper than 5 feet, armored characters may drown unless rescued)
51-55	Water, Icy (1d2 damage / turn from hypothermia until victim leaves)
56-60	Water, Boiling (1d6 damage / round until victim leaves)
61-65	Water, Contaminated (10% cumulative chance / round of catching disease)
66-70	Tar (extremely sticky, takes 2 turns / individual to extract if possible)
71-75	Acid (1d3 damage / round, destroys wood, leather etc in 1 round, metal in 1 turn)
76-80	Poisonous liquid
81-85	Gray Ooze
86-90	Green Slime
91-95	Ochre Jelly
96-00	Black Pudding

What Trap Charts?

The title of this post references a classic Alarums & Excursions zine that ran in the very early issues. Certainly in my heart I hope it was an evasive denial of real trap charts.

I love charts in RPGs. One of my favorite gaming aids is the Judges Guild Ready Ref Sheets, and I've always loved the heaps of charts in the Dungeon Masters Guide. Some of the best products of the old school renaissance are the Dungeon Alphabet and the Random Esoteric Creature Generator for Classic Fantasy Roleplaying Games and Their Modern Simulacra.

I also love traps. I think Jim Raggi's Green Devil Face is fun, and I contributed to it. My first OD&D game included what I affectionately refer to as the "bear trap" (a room with a bear in it, which provoked a ton of discussion that I cut off by pointing out that there was a bear coming at the PCs). Even the cheesy fun of Grimtooth's Traps appealed deeply to me.

So I've decided on a project: trap charts. These are going to be detailed charts to give a wide variety of options for traps. Mainly because I want to use them myself, and I've been thinking of ways to spice up traps beyond arrow, pit, arrow, pit, teleporter, etc. These essentially boil down to a simple set of options; roll or pick from the charts, and now you've got a trap with 4 knives that fire from behind a tapestry when someone makes a noise in the room.

These charts are probably going to come down somewhere from 16-20 pages without artwork, and I will want to publish them. They're pretty system neutral and I'm not worried about what system you use or branding. So three questions:

- Would you be interested in buying these (almost certainly as a Lulu publication)?
- Would you be more interested in a "Trap Charts" product, or as a chapter in a broader product called "Old School Miscellany"?
- What should I do for the art (if anything)? I can't draw but my wife can, although she isn't exactly a D&D enthusiast, but I don't exactly have an art budget.