I walked along the path for most of the rest of the day. The land trended very faintly uphill even after getting out of the small valley that Suwlahtk was built in, which gave me the impression that I was heading in the right direction. I still had virtually no idea of the shape of the island, but heading east from a western village would mean moving inward, which also meant moving uphill. The trees began to thin out towards the end of the day, changing the dense forest around me into one which let in more frequent sunlight and had more grass covering its bottom. The amount and variety of animals changed as well, with fewer insects and more birds, as well as more rat-like things scavenging the forest floor.

As the sun went down I deliberately walked off course into the woods. If they sent anyone after me I shouldn't make it too easy for them, I thought. My walking pace was quite a bit faster than the pace I saw humans in the village using, so I assumed that there would be a good distance between myself and any hunting party. However, I needed to stop to eat and drink while they would likely have rations, giving them a consistency advantage. For a moment I cursed myself for not saving my food reserves from the fire, and then again for not trying to steal some food as I left Suwlahtk, but upon thinking it over I knew it was for the best that I hadn't done the latter.

Sure enough, within thirty minutes of the road I found another stream, too thin to even be called a creek. I gulped down water, filling my gullet, then looked around for useful materials. My cordage had also been burned up in the fire so getting more of it was a high priority. While I didn't see any food, I did see some smaller reeds that were not unlike the large ones I had picked apart for cordage previously, so I got to work. Half an hour later, as the sun was setting and I was weaving together piles of plant fiber, I heard the sound of movement coming from downstream and paused to take a look.

I crept up through some sparse bushes towards the sound, then peeked out and couldn't believe how fortunate I was. Another deer, this one smaller than the one I had killed previously but still visibly an adult, was drinking from the stream. It looked directly at me for a moment, totally frozen, then continued drinking as though it believed I was not a threat to it. Do the humans in this area not hunt them regularly? I wondered, thinking back to the smokehouse in Suwlahtk, Or maybe are they just stupid enough to not understand their position? I drew my spear, pulled my arm back, and tossed, scoring a direct hit through the lungs of the deer.

The animal let out a yowling screech and jumped, flailing in midair and spewing blood everywhere before landing on its side. Unlike last time I had no intention of letting it run off and charged it with my knife drawn as it tried to get back to its feet. As I grappled with the beast it nearly gored my stomach several times with its horns, but eventually I saw an opening and stabbed its neck through the main arteries. As it bled out I held it in place with the knife and the spear, moving them occasionally to encourage blood flow to continue. The thrashing became slower, weaker, then breathing and movement stopped entirely. Now, is it actually dead? I wondered, pulling out my knife and watching its wounds carefully. No regeneration, I thought, and it took, what, a minute to die? I dragged the deer back to the pile of cordage as I added this information to what I already knew about killing animals on the island.

An hour later I had a good fire going and was roasting strips of deer meat over it. Sadly I lacked the time and the tools to properly tan the deer's pelt, as I had found out by my casual observations of hide tanning going on in Suwlahtk while I was there. The humans of the village used the brains of the animals they killed to treat the hide, turning them into a soup and plastering the mixture onto the hide after stretching. So instead of trying and failing to tan the hide again I simply removed it and discarded it, leaving it to the corpse rats or whatever other scavengers wished to have it. I pulled the piece of meat I was roasting out of the fire and chewed it, savoring the meat's taste as it filled my belly and added to my nutrients.

I need to understand more about this healing ability, I thought as I lay beside my fire. It wasn't the first time that I had thought about it, but it was the first time since I had discovered the ability and tested it on myself that I had thought about it so deeply. How did Ahpoyt survive the head wound I gave him? I wondered, How much of a brain can be safely regenerated, and in what time can it be done? My understanding of human brains was not what I would have called complete, but it included the basics. Human brain activity was a continuous, varying process that included multiple states of consciousness and unconsciousness. Generally it was robust to small disruptions, such as those from minor physical damage or chemical disruption, but once it ceased entirely it was notoriously difficult to start again. In a lot of ways it resembled the simpler circadian activity in the heart, only many orders of magnitude more complex.

Ahpoyt had sustained a head injury that should have been fatal and most certainly caused his brain enough physical damage to disrupt any brain activity severely, yet he recovered without issue as far as I knew. On the other hand, I had proof that destroying certain parts of the brain for an indeterminate amount of time caused death to the humans on the island. Can their healing actually restart their brain activity if it stops? I wondered, could that be the limit? I didn't know exactly how long, but I knew that brain activity didn't usually stop instantly on death, instead petering out over some time after what humans would normally consider the point at which an individual died.

I tried to push the thoughts out of my mind and sleep but they kept coming back. It has to be able to do that, I concluded, damage to the heart can easily stop it and yet they can regenerate from it, even keep their heart beating with an obstruction inside. Technically I was inferring that the humans could do such a thing from my experiences with the first deer I killed, but I saw no other differences between the effects of regeneration between the two species so I thought it reasonable. But then why do they die at all? I asked myself, Why can they become unconscious from injury? I frowned with my eyes closed, trying to either find an answer or sleep until the morning.

Apparently I succeeded at the latter, because the next time I opened my eyes it was morning and my fire had gone out. I shot up, looking around for anything hostile which might have crept up on me, and saw nothing. Movement to my right drew my attention once I relaxed, and my eyes drifted over to see the deer's corpse shifting around gruesomely. For one moment I was filled with shock and doubt, thinking that somehow I might have been right about the humans actually never dying. Then a furry face popped out of the deer's ribcage and I remembered digging up Ahpoyt's head. The rat turned to look at me, squeaked something, then dove back into the carcass.

Was I just lucky to have not encountered them before? I wondered as I watched the rats who had contaminated my kill eating their fill of the organs and flesh. All nine of the animals were totally unfazed by my presence, as if they believed I wouldn't hurt them. Maybe they think they can fight me off if I try it, I thought with a chuckle. Actually, this is a good opportunity, I considered, if the deer and the humans regenerate the same way, the rats might as well. I recalled how the corpse rats I had fought with when digging up Ahpoyt needed to be physically crushed to stop them from attacking me, then looked to the new bundle of cordage and had an idea.

Thirty minutes later I was chopping pieces of my skin off and dumping them near the creek to avoid getting any infections, and five very noisy and upset rats hung by their back legs from a nearby tree. The fight had been long, unpleasant, and incredibly productive from my point of view. They're smarter than I thought, I mused to myself as I thought about how the rats had begun changing their attack style once they realized what I was doing. After tying up two of them with cordage and hanging them from the tree, the remaining seven had begun using a bite-and-move style of attack instead of their normal latching style, clearly trying to avoid capture. Once I had captured the fifth rat, the remaining four fled for their lives.

“Now, we're going to do some experiments,” I said out loud in English while looking at the nearest rat. As though it knew what I was saying, it stared back at me spitefully and bared its teeth. I pulled out my knife, removed it from the branch, and got to work.

What does this even mean? I thought as I sat defeated in front of five dead rats at noon, it's so much more complex than I thought. Initially I had postulated that the regeneration took place in distinct steps, seeing the existence of two of them and inferring the existence of a third. My experiments on the rats confirmed that I was correct, but added many more questions for which I had no answers. I just don't understand why this works the way it does at all, I grumbled.

As I had figured, the first and most rapid form of regeneration was targeted at pain, though as I found out when carving up the second rat it didn't work on the organs in the chest cavity even if those organs were capable of experiencing pain. It could just be that rats experience pain differently, I thought as a counter to the evidence, but it changed little about what I observed. Skin ruptures, broken bones, torn muscles, and the like initially displayed a rapid healing effect seconds after infliction, which was consistent with the time it took an organic brain to process pain and the location of said pain. If the rat was able to see the location of the wound as it was inflicted, rapid regeneration began sooner, further strengthening the theory.

However, even if the rat was unable to feel pain due to its spinal cord being severed it would still regenerate rapidly if it could see the wound. If it could not, the wound would close more slowly but still much quicker than it should have naturally, consistent with the second speed of regeneration. So it isn't so much the pain as the sensory information needed to engage rapid regeneration at a point on the body, I concluded. The rapid regeneration was also imperfect in some ways, leaving scars on skin that did not fade quickly, and toughening other tissue. The real mystery effect had to do with the fur and nails on the rats. When cut, the fur or nail would remain cut. When pulled out, the fur or nail would grow back to full length. Even if the rats could see that a section of their body had been shaved the fur would not grow back unless plucked out. It could be that they don't see shaving as an injury, I thought, but nail clipping? It would be strange if they didn't.

The second type of regeneration was a much fuller regeneration that applied to organs and other tissues which could not, or perhaps simply were not, rapidly regenerated. Lung punctures, for example, took anywhere between twenty seconds to heal for single simple punctures up to multiple minutes if an entire lung was shredded to pieces but not removed. They could also be fatal if the creature suffocated as a result of them. Similar effects could be observed with liver damage, intestinal ruptures, even spinal damage. Heart tissue regenerated the quickest, unsurprisingly from a logical perspective. Secondary regeneration also could not, by anything other than death, be disrupted, meaning it did not appear to require the brain to be directly connected to the tissues it affected. However, secondary regeneration did stop when brain death occurred, which was odd.

What really made the second type of regeneration different was that it was nearly perfect. No scars were produced, and the regenerated tissue looked outwardly identical to the original tissue before the wound was inflicted. In cases where rapid-regeneration was suppressed through spinal injury, skin wounds that regenerated showed no scarring. It's two distinct processes, I thought, outside of sharing the same goal and perhaps the same mechanism, they are nothing alike. Additionally, my own subjective memory led me to believe that secondary regeneration likely hurt much less than rapid regeneration.

The third type which I had postulated about, and the strangest, was regrowth. When tissue was removed entirely replacements would be generated from other bodily material. What made it strange was that regrowth could be rapid in cases where rapid-regeneration was enabled but also worked on things that could not be rapidly regenerated at a slower rate. Unlike the other two healing types which largely drew on some unknown well of energy, regrowth visibly depleted other body tissues starting with fat, then working through excess skin, muscle, then extremities and finally the organs themselves.

The fourth rat, who I had stress-tested by repeatedly removing his left kidney, changed from being fat to emaciated before his wound began necrotizing, at which point his regeneration failed to work for an unknown reason. Maybe he ran out of whatever energy is represented by the blue bar on my heads-up display, I thought. I had examined the corpse after he died and, despite its anatomy being strange in general, found no hints of extra organs or implanted batteries.

The fifth rat was used for death time testing, and it was from this rat that the largest questions arose. The only conclusion I could draw that made any sense was that regeneration only halted when brain activity stopped fully, not before. What constituted “fully” was unknown, but the rat managed to survive twenty-three and a half seconds before finally dying when I severed its brainstem, dying on test fifty-eight when I went for twenty-four seconds. So when killing humans, it's probably best to keep their brainstem severed for thirty seconds to ensure complete death, I concluded, but there were more problems raised the more I thought about it. Some humans' brains could remain active for minutes after the rest of their bodily functions ceased which complicated things, and then there was the question of why.

If it can restart a heart, even regrow one, why not a brain? I wondered, it can regrow sections of a brain, clearly, so why not the whole thing? The regeneration worked regardless of conscious state, so it didn't make a whole lot of sense. I must be missing information, I thought as I washed my hands off and got to my feet, it sure would be nice to have an operator to give it to me.