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Bubble wrap is a synthetic packing material featuring small bubbles that are designed to provide cushion to the protected object and pop in place of damaging the object under excessive stress. They also make a lovely crackling sound when popped.

But this is a creation of man, and finding a layer of Bubbletastic® Extreme Guard© Bubble Paper™ across the floor or walls of a deep cavern would be... odd.

My thinking is that an organism could use this natural feature to improve its ability to defend its lair or to hunt other creatures for food.

Is it possible for nature to create renewable, poppable bubbles (i.e., bubble wrap)?

(Requested clarification) Note: I am specifically looking for a mechanism by which an environment can possess this feature independent of any animal that may or may not be living there.


Vignette

Darian crept through the tunnel. The marks along the walls were high enough to suggest they were made by his quarry. The footprints in the silt were recent, and many. Drag marks as well. Hopefully it would be asleep after its meal and he could finish it off without it ever knowing he was there.

A rush of air from ahead smelled of death and blood and... Yes! That smell! That unmistakable smell. He hurried ahead, almost forgetting to walk softly to prevent echoes alerting his quarry.

A cavern opened at the end of the tunnel. In the dim light of his lantern he could barely see the other side. And, off to the right, the light revealed the mottled brown scales of the wyvern. Cracked bones were scattered about its reclined form. The rhythmic rise and fall of its sides indicated it was, indeed, asleep after its meal.

Darian set his lantern down and drew his wyrmbane dagger before slowly, quietly, making his way toward the wyvern. When he was halfway there, however, the cavern floor unexpectedly gave way beneath his foot with a loud POP.

The wyvern's breathing quickened and it raised its head to look at the terror-stricken Darian. Before he could rush back down the tunnel, the wyvern had claimed another snack and added a fine blade to its growing treasury.

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    $\begingroup$ Are you interested specifically in bubble wrap sheets? or is covering a surface with something that makes noise in reaction to pressure good enough? $\endgroup$ – G0BLiN Dec 11 '19 at 17:18
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    $\begingroup$ Nature made humans, humans made bubble wrap, thus nature made bubble wrap. But I sense you are not looking for this answer... $\endgroup$ – L.Dutch - Reinstate Monica Dec 11 '19 at 17:19
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    $\begingroup$ @WeareMonica.The intention is that these bubbles are a feature of the environment; the wyvern in my example is merely using them to its advantage. $\endgroup$ – Frostfyre Dec 11 '19 at 17:44
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    $\begingroup$ It looks to me that you want a non-biological solution, based on the comments I below. If this is true, can you edit the question to make that clear? Personally, when I see "nature", I always include biological organisms in that category, and indeed when "nature" is used as an actor (as in "nature [creates]"), I assume it is expected to be biological. $\endgroup$ – Cort Ammon Dec 12 '19 at 15:09
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    $\begingroup$ if it's a loud pop when stepping on the floor couldn't you just use a stick or a branch snapping underfoot? Or dried out leaves being crushed? Gravel? Bio-engineered bubble wrap sounds fun but a little contrived when you can find lots of examples that do the same thing at your local park $\endgroup$ – Tom J Nowell Dec 12 '19 at 16:03

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I cannot believe that nobody has mentioned puffball mushrooms.

puffball mushroom releasing spores

They are plentiful where I am from. Basically, they blend in with the forest/natural floor, and have a hole that releases the internal spores when they are stepped on. (They can also release and crack open on their own). The older they get, the more brittle they get. Once they kind of "die" they are just waiting to release the spores. And the older ones make a distinctive sound when they are stepped on. Not a squish but a loud crackle-pop.

It doesn't sound like bubble wrap. But it can be loud if they are old enough. If I were trying to make natural bubble wrap I would start with this design and reason for functioning. It's your world, so you can change them slightly to get that effect. You could make them smaller and have them cover the floor.

The big drawback I see is this: if a creature is lairing somewhere and they use that route to come in and out, they will also deflate the modified puffballs.

I can say that from my experience, puffballs are weird in that they exist in places with wet/dry cycles. That is, they proliferate in the wet, but they do best if there is a dry cycle after. I just can't see them doing as well in a constantly moist environment such as a cave.

But I hope that this is enough of an inspiration to give you a start to creating something like this!

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    $\begingroup$ Literally just invented something like this in my own answer before even seeing this one lol $\endgroup$ – MrSpudtastic Dec 11 '19 at 21:08
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    $\begingroup$ Oh god, I had forgotten these existed at all. The last time I even so much as thought of one was 25 years ago in elementary school when children would call them stink bombs and pop them. Now I know what they are. At the time, they were something that somehow ended up in the hands of some other kid while playing in the field. I didn't even know they grew from the ground. $\endgroup$ – DKNguyen Dec 11 '19 at 22:05
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    $\begingroup$ there are also several form of crunchy lichen that could be modified to produce a blister like surface. $\endgroup$ – John Dec 12 '19 at 4:10
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    $\begingroup$ @DKNguyen Some of them aren't even attached to the ground at all. They grow there but don't even have stems connecting them to the ground, or indeed anything at all, so you can actually kick them accidentally as well. The reason why you didn't think they grew from the ground is because some variations of them you can literally just pick up, and the lighter ones can get blown around by the wind. $\endgroup$ – Erin Thursby Dec 12 '19 at 5:25
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    $\begingroup$ @J... Does it make a popping sound when you step on it? It does? Ok. That's all that is really needed. Not all species make the sound and they have to be old enough but...also, with bubble wrap, you have to purposefully pop the bubbles. If you accidentally put pressure on one, that generally doesn't result in them popping. But in the example and actual requirements, they have to be more delicate and act in a way bubble wrap doesn't generally. $\endgroup$ – Erin Thursby Dec 13 '19 at 18:11
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It is possible for nature to create the equivalent of bubble wrap. Some forms of seaweed have a vague resemblance in their air bladders:

Image of air bladders in bladder-wrack, from Wikimedia Commons

Given the correct evolutionary pressures it should be entirely feasible for an organism to develop a greater number of thinner walled air bladders so that it more closely resembled bubble wrap. The composition of the “skin” material would be probably be different in chemical composition but the physical properties could be similar.

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    $\begingroup$ Note that I am looking for a way for these bubbles to be a feature of the natural environment (e.g., a cavern floor), rather than of an organism. $\endgroup$ – Frostfyre Dec 11 '19 at 17:48
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    $\begingroup$ @Frostfyre - if your wyvren likes to eat something that grows on this "cave seaweed" (either another part of this plant or organisms found on it) but tosses the bubble leaves in its layer, you'll get your desired bubble-wrap floor. $\endgroup$ – G0BLiN Dec 11 '19 at 18:05
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    $\begingroup$ @Frostfyre If there's a beach inside the cave, the seaweed could wash up on the shore. That wouldn't necessitate an animal. $\endgroup$ – JoL Dec 12 '19 at 2:14
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    $\begingroup$ @Frosfyre: This answer doesn’t require an animal at all. Many (most!) features of a natural environment come from the organisms that lived there. The texture of a forest floor comes from shed leaves, pine needles, etc. Heathland ground is build up of compacted heather, tussock grass, sphagnum moss, etc. Similarly, your cave floor can be carpeted with the seaweed that grows there. $\endgroup$ – Peter LeFanu Lumsdaine Dec 12 '19 at 12:25
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    $\begingroup$ I can also attest that bladder-wrack really is “nature’s bubble wrap”: as a small child playing on beaches, I remember popping the bubbles in bladder-wrack just like you do with bubble wrap, including the sound of the pop. Real-world bladder-wrack is just a bit tougher and more elastic, but a fictional version could easily pop a little more easily (and more loudly, if desired). $\endgroup$ – Peter LeFanu Lumsdaine Dec 12 '19 at 12:28
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Mud bubbles

In areas of high volcanic activity, it is common to find bubbling mudpits:

enter image description here

These are driven by underground heat that boils surface water in an impermeable depression in the ground, and eats away at the surrounding stone. Once the water is all gone, It leaves behind an expanse of dried mud filled with air pockets.

From experience, walking on this dried out mud causes a cacophony of snaps and crackles as it settles under your feet, similar to walking on too-thin ice. It also reeks, because it lets out the trapped hydrogen sulfide.

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Fecal sacs.

fecal sac removal

https://en.wikipedia.org/wiki/Fecal_sac

A fecal sac (also spelled faecal sac) is a mucous membrane, generally white or clear with a dark end,1 that surrounds the feces of some species of nestling birds.[2] It allows parent birds to more easily remove fecal material from the nest.

As with birds, fecal sacs evolved as a method to clean up after juveniles by keeping their excreta in a tidy membrane sac. This approach evolved into the bubble wrap type scenario requested in the OP.

The animals litter their areas with these poo packs. The membranous wrap is the bubble. Natural decomposition of the feces produces the gas, inflating the bubble. On bursting these produce a characteristic sound and also smell; the products of anaerobic decomposition inside the sac smell bad. These decomposed and odoriferous materials usually get on the intruder to some degree, which helps the alerted animal to locate it.

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    $\begingroup$ Gross! +1 for creativity! $\endgroup$ – thanby Dec 12 '19 at 14:15
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Spores

These bubbles are spores. The spores are filled with some kind of lighter-than-air gaseous mixture or compound (possibly hydrogen - don't bring an open flame near them!), designed to carry the spores high into the air and be carried by the wind, before descending onto some other location.

Plant or fungus, doesn't matter, take your pick. The important thing is, it's a reasonably believable mechanism to make these bubbles a relatively common and entirely natural part of the environment.

The spores you find on the ground or attached to walls are spores that are almost - but not quite - matured. They're almost ready to float off somewhere, but they just haven't detached yet from the parent. Make the pressure inside the spore sufficient enough to stretch the membrane a bit, and stepping on one will produce that tiny little pop you're looking for.

Additionally, making it a fungus of some sort makes it believable in almost any location - particularly caves, basements, sewers, forest floors, or even just a particularly damp and shady wall or rock - exactly what you seem to be looking for!

Alternatively, you could drop the hydrogen(?) part of it and use something more like the puffball mushroom in Erin Thursby's answer. Instead of floating away, the shroom would just build pressure in the bulb until it straight-up explodes, causing a loud pop, an effect which would also happen should someone step on one.

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I am surprised nobody mentioned common snowberry (symphoricarpos albus). The berries give out pretty much exactly the same sound as bubble-wrap when stepped on a bit harder.

Now of course it won't grow in a cave, but

  • The wyverns may simply like them and occasionally pull some branches in to use as a snack or “side dish” or even
  • pulling them in might be an adaptation to the human attacks; depending on how intelligent these wyverns are it may be either learned, or evolved over a couple of generations from the appetite for them as the wyverns who pulled in more sprouts tended to live longer.

Symphoricarpos_albus_003.JPG

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Like Slarty, my first thought was wracks and other seaweeds or egg-pods with air bladders.

With the changed criteria ("Note that I am looking for a way for these bubbles to be a feature of the natural environment (e.g., a cavern floor), rather than of an organism. – Frostfyre"), that doesn't work. We can't even use bubbling yeasts.

In that case, there are a few mechanisms I can see.

The easiest path seems like a gas bubbling through a liquid that hardens. This has been suggested already a few times (pumice, mud bubbles).

Another mechanism is geode formation, where the forming substrate then erodes or is washed away, leaving the mineral spheres or domes of the geodes.

Another option is a solid that gets a coating, then the solid melts, leaving only the coating. An example might be a stalactite dripping into a floor, leaving a small drip-sized pit. Seasons change, ice forms, the pit freezes and forms a dome of ice (because water expands as it freezes). Seasons change more and the thaw above washes minerals down, covering the dome with minerals; the beginning of a stalagmite. The ice melts from under that, leaving a hollow mineral dome. I have not seen this, and it would require a cave that changes temperature seasonally, which isn't usually a thing (underground temps are generally fairly constant).

Another mechanism is for a liquid to harden at the top, then for what's below to go away (evaporate, etc). You see this in frozen puddles in winter: the puddle is gone and all that's left is the ice cover, that invites passing children to jump on it, and smash it like a pane of glass.

Another mechanism is for the top layer to form flat, then the mud walls to rise up under it, like a honeycomb. Again, this happens with ice in the winter, in the right circumstances

https://www.featurepics.com/StockImage/20081207/frozen-puddle-stock-image-993984.jpg

Here you see both "glass pane" and mud honeycombs.

All of these suggestions are "crunchy" rather than "poppy", however. To be poppy, you need the "mud" or "ice" or "bubbles" to be made of a more flexible material, which generally means longer-chain, biological molecules.

For that, all I can think of is tar, which still depends on the existence of organisms, albeit millions of years in the past. But if your exclusion for organisms only applies to those in the present, then you could make tar bubbles, have pitch solidify, and so forth.

[Edit: exclusion for organisms has been clarified to only apply to animals, not plants or fungi, so to me, bladderwrack seem the obvious candidate: Upvoted that answer.]

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With some luck it would be possible to create a renewing popping sounding.

Let's say you have a small pit in the ground, doesn't have to be large at all, filled with water, next something that has some rigidity falls over top the pit and forms a near perfect seal around the pit. The shape of the object over the pit is convex to allow an air bubble. When something steps on the object it flexes down and pushes the air out and forms a seal with the water, when the weight is release the object returns to its convex shape and the air breaking the seal the water underneath it to fill the gap once again creates a popping sound.

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Inspired by MrSpudtastic's idea..

FUNGAL PITFALLS

A fungus which predates animals by creating a pitfall.
Essentially growing a large hollow cavity underground, displacing and consuming any material in its path. (note that a common characteristic of fungi is their ability to

Animals then step on it, break through the thin upper surface of soil and mushroom and plummet as far as a couple meters to land on whatever non-consumable rocks the fungus left behind... They then die there, unable to escape the pit, or injured by the fall. Their remains feed the mushroom which then regrows the bubble.

The problem is maintaining soil-coverage as camouflage. My thought is that it'd grow surface-stalks, filament thin or full mushroom-caps, these would act to bind the soil to keep coverage normally, and as necessary they could hydrostatically "wave" to draw more soil over the bubble.
Their length before reaching the surface would be a factor in determining how near the surface the bubble is, as would be the weight of the material overhead.
Properly calibrated, the bubble could withstand lighter animals walking on it.
The surface stalks would also act as bait, many larger animals consume certain species of mushrooms for the protein.

For that trademark Popping noise, the bubble is sealed and pressurised with a gas gathered from nitrates in the soil or possibly just C02 from its own respiration.
This would have the advantage of suffocating the victim quickly since C02 is heavier than air.

When the victim bursts it, the overpressure should produce a loud noise, either a loud pop or a distinct deflating Phbbt noise.

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  • $\begingroup$ This sounds a little like the spice blows in Dune. $\endgroup$ – Ctrl-alt-dlt Dec 12 '19 at 9:35
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Scoria is Foamed Volcanic glass, similar to Pumice stone, but with larger bubbles.

Density varies a lot, according to the conditions when it was produced.

Sometimes this forms very large bubbles and is easily crushed underfoot.

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  • $\begingroup$ This is exactly what I was thinking. Molten rock covers the cavern floor, then rapidly cools with large gas bubbles still in it. You'd get a brittle, honeycomb-like consistency that would give way when something heavy stepped on it. The creature that lives in the cave flies over it, so the "early alert system" remains intact. $\endgroup$ – bta Dec 12 '19 at 21:18
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    $\begingroup$ This won't make a popping sound though, more like sound of breaking glass to which it is similar. Popping sound is created when the envelope is flexible and some pressure builds up before the skin tears. Which calls for something of organic origin. $\endgroup$ – Jan Hudec Dec 13 '19 at 6:24
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The mammals of nemo ramjet's speculative biology world "snaiad" have air pockets beneath their skin in place of fur, to keep them warm. This could be the function in your bubble wrap species: pockets of air that trap heat, keeping the organism warm.

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  • $\begingroup$ Note that I am looking for a way for these bubbles to be a feature of the natural environment (e.g., a cavern floor), rather than of an organism. $\endgroup$ – Frostfyre Dec 11 '19 at 17:49
  • $\begingroup$ @Frostfyre well then, no, i don't think it's possible. $\endgroup$ – Cobbington Dec 11 '19 at 17:52
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Nature has already invented this: the rafting snail makes its own bubbles from mucus to stay afloat.

The Janthinids use this bubble raft, and some species may even lay their eggs there, though it looks too exposed for predators.

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  • $\begingroup$ Portugese Man of War $\endgroup$ – DKNguyen Dec 11 '19 at 20:18
  • $\begingroup$ That's one more. The Janthinids, however, are snails which secrete a bubbly mucus. The Portuguese man-of-war uses a bladder. $\endgroup$ – Christmas Snow Dec 11 '19 at 21:05
  • $\begingroup$ Mucous bubbles don't pop audibly. Also, the cavern floor would have to be moist, drawing attention to footing and hence the bubbles, so it wouldn't work for the text snippet from the question. $\endgroup$ – toolforger Dec 12 '19 at 8:51
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Of course nature did create bubblewrap... it just had to create oil (from various sources, as yet unidentified) and trap it underground and evolve a creature capable of making machinery to make bubble wrap out of the oil. It reminds me of the SF story of an alien that crashed on a planet, breaking a part of it's ship... then manipulated the planetary life until it produced exactly the material it needed and brought it to the ship. The material being a short length of springy steel, previously used as a tie down to hold some piece of military hardware onto a pallet during WW2

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We humans create blisters. It’s not much of a stretch for them to evolve into something that can make a popping sound, or to grow without being triggered by injury.

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A similar structure that occurs already in nature is honeycomb.

Honeycomb

Honeycomb is made up of small individual cell structures arranged in a lattice, just like bubble-wrap. It does not strike me as unlikely that a colony insect might create a bubble-wrap like structure to house their larvae.

The problem here is that bubble-wrap is filled with air. We would expect the insects to not make empty cells without a reason to do so. So the question is what properties of bubble-wrap might be useful to a colony insect?

The one that comes to mind is sound. The very property that your sample story is concerned with. Since bubble-wrap makes a popping sound when it is stepped on, a colony insect living in a cave could build empty versions of their hive structure nearer to the entrance of a cave to alert the colony of intruders. (just as it alerts the dragon in your sample story, they might even have a symbiotic relationship with the dragon where the dragon deals with the intruders for them.)

We could imagine this behavior developing pretty naturally. The bubble-wrap structure might just be a version of the wax cells specialized over millions of years of evolution.

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Since you're talking about the inside of a cave, geological features would probably work best. You're going to end up with something that resembles and upside-down sheet of bubble wrap. That is: a reasonably flat surface, but with voids or air pockets just underneath.

For caves created by volcanic activity, see the good answer posted by @Ben.

Another option is to have the cavern floor made of slate, shale, or some other fissile stone. The stone naturally breaks apart into thin sheets. A heavy footstep on a weaker area could cause the topmost layer to crack or shatter. Step on an area where 2-3 layers lie on top of a void, and you could cause quite a racket.

You could also have the floor be some sort of sedimentary rock that formed when this cavern was underwater. Crustaceans lived in the mud and left their shells behind when they outgrew them. When the cave dried out, the mud hardened and the now-brittle shells formed air pockets in the rock. If the rock-to-air-pocket ratio is right, you'll have something that looks like normal rock but would "pop" and collapse when too much weight was put on it.

Some types of stone (like limestone) will dissolve in acid. You could build the cave out of a compressed conglomerate that contained large pockets of limestone. Over time the acidic groundwater dissolved away all the limestone but left the other stone around it intact, and now you have large voids that can collapse under weight.

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