When Grud finally fell asleep, muscles in certain parts of his limbs and torso, especially the muscles that controlled his joints that did most of the daily movements began to ripple and twitch. These muscles were mutating as they assimilated the rabbit’s fast-twitch muscles that would allow him faster bursts of speed.

At the same time, Grud felt a pressure in his ears that irritated him, but not enough to wake him up. His ears were also mutating to sharpen his hearing. Overall the whole mutation process was relatively painless compared to the previous mutations.

While the mutation process was going on, there was another activity going on in Grud’s mind.

—

Grud was relaxing by a lake after he just finished washing himself, when he noticed the Chieftain's youngest daughter Nita approaching him and slowly undressing herself. As he saw that, his dick quickly became erect as he walked towards and as they finally met, Grud reached out with both hands and sank his fingers into a breast and ass cheek each as Nita moaned in pleasure.

Grud did not waste any time as he pushed Nita to the ground and positioned himself between her legs. He had seen other adults having sex before, so he had a rough idea on what to do. After aligning his engorged penis to he vagina, he thrusted in all the way to the base of his dick and after he got into a rhythm of pounding Nita’s pussy, he reached out to her breast and started groping them, taking turns sucking each breast and eventually bring both nipples to his mouth and sucking them both.

And as this carried out in his mind for what seemed like many hours, out in the real world over the course of a couple of hours he emptied his balls all over himself and his shelter. Before Grud went to sleep, he took off his leather wrappings in case he got morning precum all over it again and used it as a head rest. What he got was some real serious cum on it when he woke up early in the morning.

—

As Grud woke up, he recognized the smell of his cum again and expected a light washing to get rid of the precum from his body. What he woke up to was far worse. When he got up to look around, he felt crusty on his upper body and as he looked down at himself, he noticed he was covered in his dried or drying semen and as he looked up and behind where he slept, then back down to his morning wood and his balls that were back to full capacity, he let out a long sigh. “This is really going to be a problem. Looks like I need to release a load once when I wake up and once before I go to sleep, hopefully that would keep this mess from happening again.”

After about an hour, Grud cleaned himself and his shelter up, visited the wank wall of his previous shelter to take care of his morning wood and eagerly headed out to continue his hunt for the Big Tooth Cat. The whole of yesterday was wasted testing out his new body and feeding himself.

He made his way back up the stream past the area where he found the Tusk Pig. along the way he hunted, ate a rabbit and when the sun was high in the sky, he finally found the track of the Big Tooth Cat. The tracks were headed further upstream and as he tracked along, he came upon some of its droppings. From what the hunters taught him to look out for, the droppings were three to four days old. From where the droppings were, the tracks lead deeper into the forest away from the stream.

Seeing this, he decided to cross the stream and set up camp with another shelter at a safe distance from where the droppings were located. When he was done with the shelter and gathering some firewood, it was already mid afternoon and he did not have a proper meal today, even with a whole rabbit to himself.

After an hour of searching on his side of the stream away from the Big Tooth Cat droppings, he came upon a lone deer munching on some low hanging leafs. Upon spotting the deer, Grud got down to the ground and began a slow crawl to hide himself behind the trees and shrubs while trying to keep as silent as possible.

When he was at a spear throwing range he was comfortable with, he repositioned himself into a crouch and prepared to throw his spear. When he felt he was ready, he sprang up from his cover and launched his spear at the deer. 

To his surprise, his throw was a lot more powerful than he expected and the deer was knocked to the ground but managed to recover from the shock, scrambled to his feet and ran into the forest with a spear sticking out its side. Unfortunately the hit was not so clean and managed to only puncture one of its lungs, this meant Grud had to chase and track down the deer that was bleeding out and rapidly losing energy.

After about ten minutes of chasing and tracking, he found the deer laying on the ground, gasping shallow breaths. Grud retrieved his spear from the deer’s body and with a proper thrust into its heart, the deer stopped moving after a few seconds. He then proceeded to gut the deer and bring the carcass back to his new camp.

When he got back to his new camp he proceeded to start a fire, skin the deer, break the deer down and began cooking. While he was cooking he started eating the deer’s raw heart as a pre-dinner snack hoping he got something useful from it.

When he looked at the sky, it was already late afternoon. “If eating the Tusk Pig made me grow so much, I wonder how much I would grow after this deer. If I am going to hunt this Big Tooth Cat, I am going to need to be as strong as possible.” Excitedly Grud began eating what had already been cooked and kept on putting meat over the fire as he ate.

By the time the sun was just about to set, he had finished his meal. His digestive system adapted to the prodigious speed and amount he was eating, after which he drained his water skin and went to the stream to refill his water and washup. Went to a nearby tree to do his obligatory wank in order to not make a mess while he was asleep, took off his leather wrapping and turned in for an early night's sleep.

When he fell asleep, no significant mutation took place because what he had now was better than what a deer had and was only good for biomass. The only thing that happened was that Grud’s body grew taller and was finally filled out properly to not look skinny anymore. He even got to regain some body fat that his body desperately needed. He now looked like a well built young man.

—

Deep into the night, across the stream and deeper in the forest form where Grud was currently sleeping, something was prowling its territory when it picked up a smell. It was the smell of prey blood, it was hungry, this could be an easy meal. As it followed the scent, it led to where a stream was, the smell was getting stronger, it was close. It crossed the stream and when it arrived close to where the scent was coming from, it saw light.

The light was a smoldering campfire with its embers dimly glowing, some distance to the side of the campfire was the stripped carcass where the scent of prey blood was coming from and beyond the campfire was a man laying on the ground sleeping. Easy meal.

—

While Grud was sleeping his nose picked up a smell and started twitching, soon his ears picked up the sound of grass carefully being stepped on but more importantly, the ambient sound of small creatures and insects was suddenly absent. Even while asleep, these bits of information started sounding alarms in Grud’s subconscious mind, which forced him to open his eyes and look around.

What he saw when he turned towards the campfire was a Big Tooth Cat three times his size illuminated by the dying embers of his campfire. He froze and stared at the Big Tooth Cat and the Big Tooth Cat froze and stared back at Grud. They stayed like that for a few seconds until what seemed like an unknown signal was given, they both burst into action.

The Big Tooth Cat pounced, aiming to snap Grud’s neck or crush his head in one go. Grud grabbed his spear by his side and rolled away but he was not fast enough. While he avoided getting his head and neck bitten off, he was not fast enough to avoid a follow up attack of the Big Tooth Cat taking a swipe at him. 

Even with his now far stronger and denser skin, muscles and bones, the Big Tooth Cat’s paw impacted the side of his body and sent him flying a few feet away, this swipe left him with a few broken ribs along with a nasty gash from three of its claws.

As the Grud was recovering from that impact and trying to scramble to his feat, the Big Tooth Cat pounced again. Seeing that he had no time to fully get to his feet, he braced the spear on the ground with the spear head facing the Big Tooth Cat, only for the Big Tooth Cat to impale its left shoulder on the spear and pole vaulting itself over Grud but in doing so, snapped the spear shaft in half.

Using the brief window of time that the Big Tooth Cat was stunned and trying to get to get back on its legs, Grud got up and sprinted to his shelter to grab his stone knife. After getting his knife, he turned to face a very angry Big Tooth Cat that was glaring at him with murder in its eyes.

Grud’s mind racing, thinking of ways to survive this. And now that the first round was over and the second was beginning, Gruds Fight or flight response was taking hold and after seeing half of his spear sticking out of the Big Tooth Cat’s shoulder, he remembered what the hunters told him “If it can bleed, it can be killed. We even managed to kill the mighty Mammoth” but that memory did not convince him to fight a bloody Big Tooth Cat. 

As if his mind was trying to give him a good reason to fight, he remembered the wet dream of Nita. He got half erect thinking about it, but the most important factor that made him choose the Fight response, was that he knew he did not stand a chance out running a Big Tooth Cat in the forest at night.

After the first round of the fight now they were circling each other around the smothering campfire, sizing each other up looking for weakness. The Big Tooth Cat noticed that Grud was guarding the left side of his body that had broken ribs and Grud noticed the Big Tooth Cat was favoring its left side on the count that there is half a spear sticking out of its shoulder.

Taking his chance he sprinted towards the Big Tooth Cat trying to keep to its left side. The plan was simple, stick to its left, try to stab it, retrieve his half spear to try to do more damage and if any other hunters heard of this plan, they would have smacked Grud upside the head and scolded him, but that was the best idea that came into his head at the moment.

In a sudden burst of movement, Grud sprinted to the Big Tooth Cat’s left side, the Big Tooth Cat hopped back and to its right at Grud’s sudden movement, then swiped at Grud. Lucky the swipe only knocked the stone dagger out of his hand but he made it to the side of the Big Tooth Cat and made a snap decision. From the side, he jumped on the Big Tooth Cat’s back and wrapped his arms around its neck in a chokehold and squeezed as tight as he could.

In response the Big Tooth Cat began thrashing and rolling around while also trying to reach its back with its claws. After a few moments of holding on for dear life while getting bruised, battered and scratched, Grud finally had the presence of mind to notice the half spear sticking out of its shoulder. Thinking quickly, Grud sacrificed the grip of one arm to grab the spear and ripped it out of the Big Tooth Cat earning a pained yowl followed by more furious thrashing around.

Grud managed to clamp his legs around the sides of the Big Tooth Cat’s body to stabilize himself, then started stabbing wildly at any possible angle that he could reach. The Big Tooth Cat was not able to defend from all the stabs, even by swiping at the half spear or just taking the stab with its front legs to defend the body.

While Grud was stabbing, the Big Tooth Cat was throwing itself, along with Grud, against trees, using its hind legs to scratch Grud off its body and rearing up on its hind legs and letting itself fall backwards to bodyslam Grud. This resulted in more broken ribs, almost his whole body being bruised and his legs and the arm wrapped around the Big Tooth Cat’s neck being torn up by its claws, but Grud did not notice any of this as adrenaline was pumping through his veins.

After almost a minute of struggling both Grud and the Big Tooth Cat became still as Grud was pinned on the ground by the Big Tooth Cat’s bulk. After another ten seconds or so, the arm that was wrapped around the Big Tooth Cat’s neck released the neck, followed by Grud extracting himself from under the Big Tooth Cat, walking a few steps towards the shelter and collapsed into unconsciousness.

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