Safely sinking

Surely, quicksand can't be that dangerous, an anthro fox thought to himself as he undressed next to a pool of the stuff in a forest. He, William, had always wanted to try out sinking in quicksand to see what it was really like, and now he was finally getting around to it.
Fully nude, he stood next to the quicksand, then, with only a moment of hesitation, he started walking into it. It didn't start pulling him in right away, but as he kept walking, each step got noticeably harder than the last, his feet sinking in a bit more each time. He got about halfway to the other side before he was stopped, now unable to lift his legs again, but he didn't mind; this spot was actually what he'd been aiming for.
He looked down and smiled as he watched the quicksand slowly climb up his body as he sank, going from his shins to his knees to his thighs over a few minutes. This was feeling surprisingly good, more than Will expected, the sensation of the cool muck slowly pulling him down starting to get him aroused. Even as his hips started to go under, his newly-erect cock poked above the surface for a bit longer. The fox started slowly masturbating, wanting to drag out his pleasure as long as possible to make sure he'd only climax once he'd been submerged for a long time.
Continuing to be pulled deeper, his cock went entirely under, then his chest, the quicksand now creeping up his neck. Still, Will wasn't afraid or nervous at all; there was no way it would be as hard to escape as cartoons made it out to be, and he'd always been able to hold his breath an incredibly long time. He tilted his head down to get part of his snout into the quicksand, blowing bubbles through his nose to pass the time.
Over time, he needed to tilt his head less and less, until he started needing to tilt it backward so he could keep his face above the surface. Even now, he had no fear, jacking off and still occasionally blowing bubbles. Eventually, though, even tilting his head all the way back still had his face starting to be covered up by the quicksand, and he had to close his eyes, his snout being all of him that was still above the surface. He didn't even raise a hand in hope of being rescued; he was confident he wouldn't need it.
Another minute, and even most of his snout was under. Not wanting to just wait for himself to sink that little bit farther, he took a deep breath through his nostrils and lowered his head. Now, the only signs the fox had been there were his clothes on the shore and the few bubbles coming up from where he'd gone under. He was still relaxed, holding his breath and jacking off, enjoying the coolness around him.
Several minutes passed as Will continued to sink, getting farther and farther from the surface. It wasn't an issue, he could just swim back up once he needed air, but that wouldn't be for quite a while yet. He released some bubbles in a moan of pleasure, the quicksand almost massaging him as he sank.
Eventually, having been below the surface for 8 minutes, the fox felt something solid under his feet. He'd sunk to the bottom of the quicksand pool! While he had no idea how deep he was, he didn't mind, still confident he could get out on his own once he needed to. Pulling up his legs, he sank some more for about another minute, landing on his butt and sitting down on the bottom. While he was feeling the need to breathe by now, it was still going to be a long time before he badly needed air, and he intended on making the most of it.
His breath hold progressed into the double digits, and even well into the 'teens, and Will was starting to struggle. He was also finally getting close to an orgasm, and even having held his breath for 17 minutes, he didn't want to go up just yet, still wanting to cum before that. Thankfully, it didn't take much longer; one more minute, and he tilted back his head and moaned as he came, shooting an impressive amount of cum into the quicksand.
Finally, the fox had had enough; his chest was heaving and his lungs burning. It was high time he got back to the surface. With more effort than he was expecting, he stood up again, and jumped from the bottom to swim. His strokes were slow from how dense his environment was, and soon enough, he just sank again, feet hitting against the bottom. As he started getting nervous, he tried again, with the same result. And again, and again... This wasn't working. He couldn't swim out of here, he was going to drown!
Covering his mouth, Will briefly opened his eyes to try to see if anything around could help. Not only could he not see anything through the opaque quicksand, it hurt his eyes, which he quickly closed again. With swimming being out of the question, he started to just walk on the bottom instead, at a frustratingly glacial pace that, deep down, he knew wouldn't get him out in time.
The 20th minute hit, and the poor fox shivered as he did everything he could to keep holding his breath. But, finally, he just didn't have a choice any more. He doubled over, bubbles repeatedly erupting from his mouth even as he still tried to cover it. Too soon, he was out of air, and his hands dropped from his mouth as he finally took a huge gasp, flooding his lungs to the top with mud...
...Except, it didn't hurt. He didn't choke, or cough, or anything, just breathing freely. Not only that: He felt fine! The urge to breathe was entirely gone after just a few breaths, and here Will was, breathing quicksand as if it was air. Dumbfounded, he took a few more experimental deep breaths, and apart from how much more effort it took to breathe this than it did air, it felt perfectly normal to his lungs.
Worried this strange ability might eventually wear off, the fox continued very slowly walking to get out of the quicksand. It took ages; a minute of effort would only move him a couple feet, and he couldn't tell where he was going, so, unknown to him, he went in circles for quite a long time. Thankfully, he remained able to breathe the whole time, and after nearly an hour of work, he finally noticed things getting brighter past his eyelids. It didn't take much longer from there for him to get to the surface, his mud-coated head finally sticking out.
As he exhaled again, quicksand erupted from his nostrils, which of course felt weird, though still not unpleasant. Climbing the rest of the way out, he spat up what was left in his lungs as he finally got air in them again, for what little it seemed to matter. After mostly cleaning himself off, Will looked down at the quicksand again, and decided to test whether being able to breathe it was just a fluke, sticking his face under again and inhaling. His lungs flooded, and again, it felt fine, not even slightly hurting.
Pulling back, he exhaled the mud back out again, and wiped his face. He'd have to do some research on this at some point, to figure out what had made him able to breathe the mud and see if it applied to anything else. Rounding the quicksand pool, he dressed himself again, and started on his way back out before happening across a pond.
Deciding to get a head start on his research, Will dipped his face into the water like he had with the quicksand and took a breath. Even the water was perfectly breathable to him! "How is- Woah, what?" Not only could he breathe, he could talk perfectly clearly! "Oh, this is so cool!" He stood up again, exhaling water, now with even more questions as he continued out of the forest.