Let’s talk about Super Mario World. Just briefly. Because you can’t talk about traps in RPGs – which is what we’re talking about – without talking about dick moves and screwjobs. Super Mario World was the sequel to Super Mario Brothers 3. If you don’t know the bros, I honestly don’t know how to help you. Because the whole Super Mario Brothers thing is huge. That’s like not knowing Disney.

Anyway, in 1990, Super Mario World was released as a launch title for Nintendo’s new 16-bit console, the Super Nintendo Entertainment System. See, back in the day, bits were the equivalent of frame rates today. It was all about how many bits you could pack into your video game. Whatever that actually meant. Anyway, Super Mario World was AWESOME.

But 17 years later, 16-bit games were basically ancient. You could pretty much run them on a pretty good graphing calculator. And so, most people who were playing Super Mario World in 2007 were playing it on emulators. An emulator is a computer program (that my legal department is insisting that I remind you is highly illegal and every time you emulate a video game, an orphan puppy dies) that pretends to be a video game console and lives inside your computer. You can run the games of yesteryear inside these emulators and play them just like you could in the old days. As long as you don’t mind using an X-Box controller with a tiny – though noticeable – amount of delay because USB technology is crappier than those controller plugs that basically involved jabbing metal pins into plastic holes.

But I digress. With emulator technology came the advent of the save state. A save state is kind of like saving your game. But instantly. At the exact moment you press the button. When you load the save state, the game resumes exactly the way it was when you press the button.

Now, these older games were not designed for that crap. Some of them couldn’t save games at all. Some restricted where you could save your game. Some used passwords. And while these were the result of technological limitations, game designers knew that s$&%. And so, they built their games around the knowledge that a player couldn’t instantly save and reload and save and reload.

So, in Japan, in 2007, you had these dudes, R. Kiba and T. Takemoto. And they were looking for a new challenge. Because, once you can save state, the games of old lose a lot of their difficulty. Being able to instantly, with a single button press, try and retry and retry again removes a lot of the penalty for failure. So, Takemoto took Super Mario World and created Kaizo Mario World. Basically, he made a new game out of the same assets as Super Mario World. But it was based very heavily on trial-and-error style gameplay, memorization, and surprise traps. And it was fiendishly difficult. By the way, Kaizo just means “remodeled.”

So, imagine you start playing. You take one step and spikes spring out of the ground. Wham. You’re dead. Restart the level. Or, you just reload your save state. You’re instantly back in the action and now you know where the spike trap is. You try to jump it. You hit an invisible coin block. And it deflects you into the spike trap. And slowly, surely, you figure the games tricks and traps out. Because you can play over and over again. And each time you have to deal with a trap, you have a little more knowledge of how to deal with it.

Now, Kaizo Mario World lead to the creation of I Want to the Be the Guy and I Want to Be the Guy Gaiden by Kayin Nasaki. And those games imposed more control over when and how you could save. In a sense, they expanded on the basic problem of how you can have challenge in a game in which death is basically trivial. See also: Super Meat Boy. But Kaizo Mario World also lead to the creation of THOUSANDS of crappy super hard dick platformers by people who kind of missed the point. And they turned the word Kaizo into a f$&%ing genre. And s$&%ed it up bad.

What’s the point of all of this? The point is that the mechanics of your game determine what you can and can’t get away with. And they determine how you have structure challenges to make them interesting and fun. Because challenges always have to walk a knife’s edge. Teeter too far to one side, you fall into the abyss of boringess. On the other side, you plunge into the meat grinder of frustration. And players will adapt their play style to optimize their ability to deal with challenges.

And THAT is why traps suck in D&D. They do. They utterly suck. Traps are a weirdly iconic part of dungeon delving. And yet, they always suck. So, today, we’re going to talk about why they suck and how to maybe make them suck less{@.(]#!…}}/HOLD ON! This is Angry from the future cutting in. Well, not Angry from YOUR future. It’s Angry from your past, but Angry from the future of when this article was written. See, here’s the thing. I had this whole article all ready to revise and post. But I was pooping and I started thinking more about traps. Because pooping is the best time for game design. And I realized you could probably handle traps differently in D&D and make them kind of cooler. So, I realized I should probably tack on a rules hack at the end of this article before I posted it. And that’s just what I’m doing. So, I’m cutting of the rest of the setup here and jumping in to the content. I’ll still keep the s$&% about why traps suck and how to use them better. But I’m going to add a whole extra bit about maybe changing how you deal with traps on a fundamental mechanical level. Okay? So, forgive the abrupt transition.{%.>,|)…

What Even Is a Trap

So, what is a trap? In D&D I mean. Go ahead, try to answer right now. Try to come up with a definition of a trap that pretty much encompasses them all and manages to be useful. It’s actually tricky, right?

A trap is basically an automated attack against a target that is triggered by the target doing a particular thing. Now, I don’t mean attack in the “deals hit points of damage” sense, though it can. I mean, an attack in the general sense that it attempts to harm, hinder, kill, or inconvenience. Step in the wrong spot, an arrow shoots out of the wall and kills you. Open the chest, poison gas sprays in your face and gives you a penalty for six hours. Touch the idol, and bars fall over all the doors, trapping you in the room with flesh-eating evil weevils. Open the door, a gong sounds, summoning the ogres to throw boxes of flesh-eating evil weevils at you. Whatever.

In game terms, a trap has a few simple components. First, it has a trigger. When someone does a thing, the trap goes off. Second, it has an effect. When it goes off, this is what it does. Third, traps often have inbuilt countermeasures that determine how the trap can be detected and how it can be disarmed, avoided, or otherwise dealt with. In game terms, a trap is a simple if/then statement that can be broken under the right conditions.

Now, the mechanical pattern for traps in the game has evolved somewhat. It used to this. If there was a trap somewhere, the thief in the party had to spontaneously decide to search that particular somewhere on the off-chance it was trapped. If it was trapped, the thief would roll to see if he found the trap. If he found the trap. The thief could disarm the trap with another die roll. If the trap was not discovered or disarmed, the party would blunder into the trap and something terrible would happen. Usually, someone would get stabbed or poisoned or plunged into a pit or killed by fire.

Now, I should point out that all of this COULD be short-circuited. That is to say, if a character carefully examined the walls and found the holes from which darts would shoot, the character could deal with those. Even if there was no explicit search and disarm going on, even if the party didn’t bring a thief, someone could hold their shield up against the holes while they opened the treasure chest. Basically, they are GUESSING that the chest is trapped and will trigger SOMETHING to come out of those holes. That’s TOTALLY FINE. In fact, that’s good. But mechanically speaking, that’s something the GM brings into the game with smart trap design and clever description. I’m talking about the base mechanics here. What’s built into the system for ALL traps.

Nowadays, D&D traps are a little but more complicated. Mainly because of problems that I’ll discuss in a moment. The current process for traps goes something like this.

1. The party enters an area with a trap. There is some automatic chance – governed by Passive Perception or just by Taking 10 on a Perception check as part of looking around the area – they will notice the trap. If they do, the GM alerts them to the presence of the trap.
2. If the party doesn’t automatically notice the trap at a casual glance, they can purposely choose to take a few minutes to search an area for traps. Now, the rules that govern this are kind of vague. So, GMs tend to go their own way in a few different spots. First of all, some GMs assume a single search covers a broad area and everything in it. Others assume you have to search specific objects OR you can search the floor and walls which leaves out the objects.
3. If the party discovers the trap. They can attempt to sabotage the trap. There are skills and spells that cover this. Depending on the GM and how clever and analytical the players are, they can also attempt to avoid the trap or spring it without resorting to magical or mechanical sabotage. Some GMs ignore that. Which is frankly bulls$&%. But whatever.
4. If the party fails to notice, discover, or sabotage the trap, the trap goes off. Whatever it was going to do, it does. It might need to make an attack roll or force a victim to make a saving throw. Or the effect might be automatic if it doesn’t affect a character directly, like an alarm or a door that seals up or a bridge that collapses. Whatever.

So, that’s the basic process for a trap in D&D and Pathfinder. And it’s a really bad process for a role-playing game. Most GMs hate traps. And most players expect them. And also hate them. And yet, because of the genre and because of Indiana Jones, GMs use traps all the time. Let’s talk about the problem in the trap process.

Why Traps Suck in D&D

Let’s look at traps in D&D. First of all, how do you spot the signs of a trap in D&D? Well, if we’re in modern D&D, your character, if your character has a high enough passive Perception, the GM tells you “there’s a trap over there.” But what if you don’t? Because that process doesn’t actually involve you making any decisions. That’s just the GM telling you that your character was alert enough to spot a trap.

But let’s say you don’t. Now what? Now, you have to spontaneously decide to search for traps. You have to search a particular corridor or room or door or chest or idol or anything else that might have a trap. And when you decide to search for traps, the game stops. Why? Because a die roll is needed. Remember, die rolls to resolve action break the narrative. They are necessary, but they do break the flow.

Either way, though, in most games, there’s really only two strategies to searching for traps. First, there’s guessing blindly. “This seems like a good place for a trap, let’s search here.” “The last chest had a trap, let’s search this one.” While blind guesses are still decisions, they are decisions that, in the end, rely on luck. They don’t feel as good as decisions based on actual thought and cleverness.

The second strategy is to search absolutely everything that could reasonably be trapped. Now, this isn’t actually a decision either. I mean, it technically is. But if the party has the freedom to search everywhere and there are no consequences for searching everywhere, in a world where traps exist, not searching everywhere is stupid. But searching everywhere has the problem of slowing the damned game right down. In point of fact, that is precisely WHY the designers of D&D added the whole Passive Perception bulls$&% in 4E.

But GMs responded to that Passive Perception nonsense by setting the Passive Perception requirements high enough that players didn’t just automatically spot all the traps. Because automatically spotting the traps isn’t interesting either. It’s just the GM pointing and saying “there’s the trap, fix it.”

Once the trap is found – either automatically or as a result of a good die roll – the next step is what to do about it. Well, there’s skills and spells for that. If you know the trap is there, the rogue or whoever disarms it. If they succeed, the trap is a non-issue. If they fail, usually, the trap goes off. But choosing to disarm a trap using the proper skill or spell isn’t really a decision either. It’s no more a decision than using your keys to open your front door. That’s what they exist for. The only time things get interesting is when the party doesn’t have anyone who can handle a trap and they have to find clever ways to deal with the trap aside from throwing d20s at it. But, most parties make sure someone can handle traps. And most GMs stop putting traps in their game if no one in the party can deal with it.

And what about when the trap goes off? Well, that’s not particularly interesting either. At that point, the fates of the players are entirely in the hands of the dice. The trap happens, dice are rolled, someone gets hurt or killed, end of story. Very rarely, a trap will allow a decision like “which side of the portcullis do you want to end up on?”

Do you see what I’m saying? When you really break it down, traps kind of suck in RPGs. And do you want to know what makes traps suck the most in RPGs? It’s the fact that RPGs are games of pure imagination. Yeah, I said it. Pure imagination is really bad for traps.

The Awesome Traps of Dark Souls

There’s an awesome video game I talk about all the time. It’s called Dark Souls. And it’s awesome. If I didn’t already say that. In one section, you go through this trapped fortress. And there are two traps in particular you have to deal with. First, there are these arrow traps. And they are triggered by pressure plates in the floor. Step on the pressure plate, you hear a click, and an arrow shoots into your face. Second, there are mimics. Mimics are creatures that look like treasure chests. But, when you open the chest, it turns out it’s actually a carnivore. And it eats your face.

Now, these SEEM like dick moves, don’t they? You’re just walking along and WHAM! Arrow in the face. You open a box and instead of treasure, you get strained through the digestive system of a creature with a ridiculously improbably evolution. But they aren’t. And here’s why.

First, if you pay attention, you can see the pressure plates for the arrow traps. And the holes in the walls. They are hard to see in some places. They purposely get hidden in harder and harder places. But you can respond by slowing down a bit and paying more attention. Sometimes, you miss one. But you can almost always see them coming if you are really attentive. The same is true for the mimics. If you look very closely at a mimic, you can see that the treasure chest is breathing. It very slowly, very faintly inhales and exhales. It’s really hard to spot, but you can see it.

And that’s pretty f$&%ing cool. Or rather, it makes you feel pretty f$&%ing cool. It makes you feel like Indiana Jones. Because you’ve learned the environment and paid so much attention that you saw the trap coming and avoided it. Or dealt with it. You – the player – are actively learning and recognizing the signs of traps in your environment.

Second, when you do trigger an arrow trap. You hear it click. You have a very brief span of time to do something. Even if you didn’t see it coming, that tiny span of time can be enough to get your shield up or roll out of the way or sidestep the trap. Of course, if you don’t know what direction the arrow is coming from, you’re making a guess. But it’s better than no chance at all. You still feel like you have an active say in defending yourself. You’re relying on making a lucky guess, but you – the player – still have some agency over the outcome.

Now, notice that Dark Souls only deals with the first and last part of traps. There’s no disarming traps in Dark Souls. If you notice a trap, you either avoid setting it off or take precautions to mitigate the trap. If you don’t notice a trap, it goes off and you react as quick as you can.

But, in D&D, there’s really no good way to deal with that first issue, is there? It’s kind of a problem with the narrative structure of D&D. There’s no way for the GM to SORT OF hint that there’s a trap in the area. Is there? Well, actually, there is. And it’s the first way to go about fixing traps in your game. As for the third, in D&D, once a trap has gone off, there’s not a whole lot to decide. Is there? Well, again, there can be.

If You’re Going to Murder Someone, Premeditate that S$&%

First and foremost, I’m going to say this: you’re probably better off removing traps from your game entirely. They really do kind of suck. And if you’re going to do that, let the players know, so they don’t waste resources learning how to deal with traps. Though, in 5E, that’s not as much of an issue because (A) the trap rules are a confused, semi-contradictory mess and (B) there’s no skills for dealing with traps directly, just thief tool proficiency which also lets you bypass locks.

But if you like traps – AND I DO – then the alternative is that you have to be really thoughtful about them. You can’t just throw them in. They have to be as deliberate as any other encounter in your game. Otherwise, you’re going to train your players to search everywhere or just teach them that sometimes, randomly, they are going to be screwed and there’s not a hell of a lot they can do about it. Neither of those leads to fun.

But deliberate traps can be pretty cool. And it relies on a push and pull between two things. First, empowering the players to guess where the traps are. And, second, providing consequences for searching for traps.

How to Scream “Here There Be Traps”

Recently, my players were exploring an ancient tomb. As they walked along a hallway, they came to a place where seismic activity had damaged the masonry and exposed the bare rock behind the walls. The hallway was a disjointed ruin. It seemed like just flavor text. And then, an arrow trap! Click! Wham! Ouch!

After the arrow trap went off and healing spells had been administered, the players searched for the trap. And they discovered the trap was a simple trip wire and hand crossbow that been hidden amongst the rubble. It wasn’t part of the original tomb. It had been added and concealed by the damage. The player put it together very quickly. The current tomb robbers (which the players had been sent to deal with) had set up traps so they could plunder undisturbed. And they could only set traps where the damage to the dungeon allowed them to conceal traps.

WHICH IS EXACTLY HOW I PLANNED IT.

Sometimes, it takes players a few tries to figure out the patterns in my trap placement. Sometimes, they never stumble on it. But there is ALWAYS a pattern to my trap placement. And, right off the bat, I try to warn players about the traps. Sometimes, they will encounter a sprung trap and a corpse. And they can examine the trap carefully and figure out the clues. Other times, I will place a trap in a place where I know they can survive the trap and retreat if need be. That tomb trap was literally the first encounter in the tomb. It was basically just inside the door.

You can do this any number of ways.

For example, imagine you have a dungeon that contains traps. When the party walks between certain statues, spears shoot out of the floor and stab them. The trap isn’t in the statues. And the dungeon is full of statues. And many statues don’t have traps nearby. But the traps always come between statues. If the players examine the statues, they will discover that the ones near traps have their swords and shields reversed. They are left-handed. If they don’t ask about that detail, don’t reveal it outright. But they will probably be nervous about walking between ANY pairs of statues for a while.

You want several layers of detail is the point. There should be a detail that warns that there COULD be a trap if they pay attention to the flavor text. And then you want another layer of detail that gives a more specific answer and makes it really easy to guess where the traps are. That layer of detail is the one the players have to ask about. They have to stop and purposely examine things.

And this actually makes logical sense. Remember, when someone builds traps, they need a way around those traps. Even if it is just so they can get out after they finish arming the traps. Visual clues, hidden switches, tiny details that only they know to look for? Those are the equivalent of a password system.

And traps are expensive and time consuming to create. No one puts traps everywhere. They put them where they will do the most good. Or harm. Depending on which side of the swinging blade you’re on. In my tomb, for example, the raiders were kobolds. Classic trap builders. And there were some passages of the tomb where the ceiling had collapsed and they were in bright sunlight. Kobolds hate sunlight and they are dazzled by it. Those are the hallways they couldn’t guard or patrol. And that’s why they set traps along those halls.

See? It’s very deliberate.

If you place traps at random in your game, you teach your players that there’s no art to finding traps. They either have to guess randomly or search everywhere. If your traps are deliberate and telegraphed, and if they reward attentive players, they are interesting. They are fun. They teach the players that you will reward them for being attentive and smart.

Searching Everywhere is Boring!

If you have a world of traps and your players can freely search for traps, they WILL search everywhere. They won’t think about what they search. They will just assume everything is a trap. And that’s not fun. The players don’t actually ENJOY doing that. They do it because they feel like they have to. And they know they can. And they know it’s the safest way to handle traps. Don’t let them.

It’s important to make searching for traps inconvenient and time consuming. Because, honestly, it IS. Searching for traps isn’t a quick and easy process. It involves going carefully over details. It involves crawling around. It involves tapping things. Its detailed and its boring. And it should feel that way.

The problem is, the narrative structure of D&D removes the inconvenience. Because the ten minute, arduous process of carefully searching a section of hallway for every conceivable trap trigger can be hand waved with a simple clatter of dice and the announcement that you find nothing. And that’s a bad thing. You want to bore the players with searching for traps.

So, every time the players search for traps, describe it. Before you let them roll a die, give them the spiel about how they “carefully and meticulously search for trip wires and hidden pressure plates and strange runes. And after thoroughly going over the entire area, they find… [roll dice]”. Every. F$&%ing. Time. Two sentences are a lot of slog for a narrative game like D&D. And it discourages players from searching every square inch of the dungeon in exactly the same way that the characters in the world would get discouraged and bored. Seriously.

Now, on top of that, it’s also cool to have the passage of time mean something. If you use wandering monsters in your dungeons, that’s a perfect deterrent for searching for traps in every square.

The point is to make searching costly so that players will try to do it only when its smart. That will encourage them to pay attention to the details you’ll be providing.

Keep It Simple Stupid!

Part and parcel with telegraphing is to limit yourself to using just one or two types of traps per location. Again, this makes logical sense from a trap construction standpoint. But, more importantly, it allows you to telegraph things and teach the players what details to pay attention to.

But it also means you can have a little fun. Once you’ve figured out what traps you’re going to use and once you’ve put a few of them near the beginning of the adventure so the players can learn about them, the challenge is for you to find increasingly interesting ways to use those traps. The first two traps should be boring and straightforward. After that, they should be placed where they are increasingly difficult to deal with. You still have to follow whatever rules you’ve established for where your traps are going to go. It becomes a game. Within the rules you’ve established, how many different ways can you use a trap?

For example, the third arrow trap in my tomb was in a ruined and overgrown room that had some tiny lizard monsters in it. The lizard monsters were freely wandering pets of the kobolds. Guard beasts. The party killed one. The second one fled. And the party forgot that ruined sections of the dungeon might have traps. As they gave chase, they got arrowed. And they knew immediately afterward that they had screwed up. Now, there are better examples, but I can’t share them yet because the players are still in the dungeon and they might be reading this.

See, here’s the thing. Challenge is a constant push-and-pull. You have to empower and then you have to ramp up the difficulty. You give the players the chance to learn how your traps work, then you figure out how to screw them.

For example, imagine the party is tromping through an adventure that has two different types of traps. The first is pockets of gas that flare up when ignited (and are also poisonous). The second is gouts of flame that come out of certain statues. Now, imagine the dread when they come to the statue room that smells like poison gas.

Or imagine there is a dungeon filled with lightning traps. And, at the end, there’s a flesh golem that is empowered by lighting. And he spends half the fight trying to move to the trap triggers to power himself up. Of course, the party only knows that flesh golems like lightning if they know about golems (Arcana) or they find a particular book hidden in the dungeon. You see how all of this works? It’s all deliberate.

It’s important to remember, though, not to add traps to a combat until the party has had a chance to deal with traps outside of the combat. Some GMs will tell you the best place for traps is inside of combat. Those GMs are wrong. Because traps are just a screw job in combat. “Surprise, you stepped in the wrong, f$&% you!” Fun, fun, fun.

The Trap that Changed the World

Some of the best traps, though, are not the ones that fire-and-forget. Arrow traps and lightning traps are fun, but the best traps are the ones that create or change the situation. The classic example is the collapsing ceiling or portcullis that splits the party. Or the collapsing floor that leaves a massive pit blocking the party’s known means of escape. And there are traps they seal the players into rooms and fill with water. And piranhas.

In general, those traps – the ones that don’t directly attack – don’t need to be telegraphed. Because they provide more decision points if they actually DO go off. Sure, the party can still detect or disable them if they get lucky. But if the trap does go off, the harm it does is indirect. It creates a problem situation.

The biggest of these are the encounter traps. Those are the puzzle-room type s$^% that Indiana Jones is famous for. Like the slowly crushing walls or the room filling with whipped cream. Those are the ticking time-bomb traps. And when you design those, you aren’t really designing a trap. You’re designing an encounter. And that means, you need to design a f$&%ing encounter. Dramatic question, sources of conflict, decision points, everything. You know how to do that already if you’ve been reading long enough.

The Point

Let’s wrap up by addressing a major mental problem that GMs have with traps. Because most GMs are actually kind of dumb. Remember how I mentioned how GMs countered the Passive Perception thing by setting the Perception requirements high enough that traps never got automatically noticed. That’s because GMs secretly feel like players finding and disarming traps is cheating. Well, not really cheating. But it feels like the players are getting away with something.

See, D&D is a game about attrition. We’ve already talked about that. The major source of challenge is in managing your resources efficiently. You have to have enough HP and spells and potions and ammo and things to get through the day. If you don’t, you have to retreat or you die. One or the other.

The problem with traps is that they are “all or nothing.” If the party detects and disables the trap, they get away without expending ANY resources. And that FEELS wrong. They are supposed to drain resources. By the same token, most GMs also feel that traps should give the PCs experience points. But, if the PCs don’t take any damage, those experience points haven’t been earned.

But that ISN’T the point of traps at all. If you are viewing traps like a resource tax, like something the party should have to suffer, you’re already using them badly. A trap is a challenge that the party can overcome with 100% efficiency. That is to say, if they are smart and deal with it properly, they get all the XP and none of the resources. A trap is like the goddamned Daily Jeopardy. Double your money or lose a bunch, but no one can steal it from you.

You HAVE TO have that mentality. They don’t work any other way. Traps already pretty much suck and should be used sparingly. You can’t tack that emotional baggage on them too.

So{/:>//)ANGRY FROM THE FUTURE HERE! Remember me? This is where I had originally rambled out a conclusion. But I’m chopping off that conclusion and I’m instead proposing something else. Something that only occurred to me during my morning pre-revision poop. Sorry for the abrupt transition.

The CLICK! Rule

Okay. I’m going to crank this out fast. And I admit it’s just a half-formed idea and I really need to play with it a little. But I’m offering it so YOU can play with it too.

Remember how I said that the part when a trap resolves is completely devoid of decisions? The trap just rolls an attack roll or you roll a saving throw and then terrible things happen? And remember how I said how Dark Souls had that bit where you could react to the “click” of an arrow trap? Sure, sometimes, you were acting blindly, but it still felt like you had some say.

Imagine this.

In that split second, in that moment between when a trap is triggered and when it goes off, you ask the player “what do you do?” You don’t tell them anything about what’s going on around them except that they triggered something. They caught a trip wire. They stepped on a pressure plate. Or the lid of the treasure chest caught for a moment and then clicked free. And then you say “what do you do?”

Now, take their answer, whatever it is, and figure out whether it would actually help them avoid the trap in a remarkable way OR if it would make them less likely to avoid the trap OR if it would have no effect at all. If it was an exceptionally GOOD reaction, give them a bonus to avoid the trap. If it was an exceptionally BAD reaction, give them a penalty to avoid the trap. And if it’s a normal response that really isn’t anything special, just let them roll normally.

For example, if the trap is a scything blade that swings out of the ceiling and the player dives to the ground, laying prone, that’s a really good reaction. Right? Chances are good that the trap will swing right over them. The trap can roll with disadvantage on the attack.

But if they instead roll forward or raise their shield, those are normal reactions. That’s already included in armor class, right? Dodging and using a shield are part of armor class.

And if the trap was a collapsing floor trap and they hit the deck, laying prone, well, that’s going to give them disadvantage on the Dexterity saving throw. The worst thing to do when the floor falls from under you is to lay down on it and cling to it as hard as you can.

Sure, most of the time, the players will be guessing blindly. But if you’re also telegraphing your traps, they might make really good guesses. In fact, those aren’t guesses. They are drawing conclusions and then acting on those conclusions. Which is precisely what you want players doing.

Either way, this extra little CLICK rule gives the players just the smallest feeling of agency after the trap goes off. And it might improve traps immensely.