Prologue
At first, the half dead animal fought back. It made a guttural, whining sound in the back of its torn throat as the figure tried to pick it up with its teeth. The animal's claw had managed to find purchase in the figure's cheek, lifting off a flap of it that pooled blood. The figure fell back a moment, taking the time to feel the slick blood dripping down its face. The frantic scraping noises the animal made as it dragged itself along reverberated off of the cave walls. It was trying to get away.
The figure sat down and tore off the flap of skin that used to be its cheek, folding it into his mouth. Chewing on it like gum, he waited patiently and listened to the ragged breathing of its prey. He had hunted like this many times before. The caves were his home, and he knew the animal would just get lost and lose its strength. Then all he had to do was follow the breathing and panicked sounds of fear deeper into the cavern. The animal would be too wasted to fight back, and it would be a simple matter to twist its neck in two. That was his favorite part; the blood pouring out of its neck while he suckled at it like a newborn at a teat. Depending on the size of the animal, there was more blood than it could drink, and it would drip in waves over his body. He especially like the slick feel of it as he rubbed it into his pale skin.
He was getting hard just thinking about it now.
He grunted in anticipation, swallowing his own flesh in one gulp. Sitting up on his haunches, he felt around in the dark with a ragged claw. He didn't need any light to find a nearby rock. Testing the weight of it, he felt the sharpest angle of the rock and grunted in satisfaction. He had used this rock before.
Locking in on the dragging and whining sounds, he turned his head and sat back down, He knew the game had just begun, and had a while to wait before heading out to that offshoot of the cave for his prize. The animal had seemed big, and its breathing wasn't shallow and panicked enough. Still, he was unable to stop the impatient whine that escaped his lips. He was hungry. Closing his eyes, he remembered the feel of the blood sliding down his chest and couldn't help but touch himself. He swayed back and forth in the darkness, whining in pleasure as he waited.
When he was done, he shook the semen off his hand and listened carefully. The animal hadn't made it very far. He could hear the shallow breath that he had patiently waited for and grunted as he sat back up, reaching for the rock again. His stomach growled in agreement and he patted it absentmindedly, wiping away the last bit of semen that had landed there.
It didn't matter that he was being loud as he scraped along the cave, because he knew the animal could no longer escape. Usually, he would creep along in the darkness and surprise his prey, relishing the surprised cry it would make. But now he just wanted to reach the animal while it was still alive. Its breathing was becoming much shallower now. He hoped it was still alive enough to squeal when he twisted its head off. It wasn't as much fun if they didn't squeal. Laughing in the back of his throat, he continued on his way, scraping the rock across the floor of the cave. His laughter bubbled up from a dark, primal place within him. He was enjoying this.
He knew he had come across the animal when he could see the bright panic in its eyes, illuminating the cave. There was no light to speak of, but his eyes were used to using any light it could to his advantage. For some reason, the fear in his prey's eyes always seemed to give off a light of its own. His simple brain tried to wrestle around this fact as he shuffled closer to the heap of the animal lying in the corner. Its breathing was quick and short now. He had to hurry.
Bringing the rock down on its head, he held back, not wanting to kill it. He heard the slump of its head, and dropped the rock aside. Picking up the head from the dusty floor, he caressed it for a moment, like a delicate flower. He reached up and twisted with his other hand, smiling when he heard the satisfying crunch of its neck. Twisting further, his determined grunts soon turned to guttural laughs as he set to work. He wanted to feel and taste the blood; to play with it in the darkness of the cave.

I'll say something more on
I read it, too. I'm one of
You used the word "guttural"
Also, you pay very specific attention to all the different sounds he's making. For a prologue, it felt a bit too focused on his noises. Personally--and I haven't read anything else of your story yet but if this is going to be an action story/plot driven--I think I'd speed up the prologue if this is all that's going to be in it. I'd cut out a bunch of the repeated details about the cave and how impatience he is and just get to the kill. Show the reader what he's diong, have him do it and then start chapter one. Nice, neat, clean.
Okay I don't have a terrible
The "feeling around" even though he can see in the dark is a little strange, and I found that you could have added in that he didn't even have to look, he knew the cave so well, or something like that.
I think it was a little strange that even though he had already had one part of his body removed he decided to follow my motto (when in doubt...) and whipped it out, even though it seemed to be a dead end up ahead meaning that he could have quite easily had a quick and painful amputation... not exactly very menacing...
Also, (although I haven't read enough to judge the tone of the tale) I thought that casually whipping it out made the character rather comedic in what I would have thought would have been a scary scene. I found my self only being on the edge of my seat because I had to wipe a small tear of laughter away. The contrast may work, but I have to read more to tell...
I like the fact you did focus
However watch tenses in sentences:
He especially like the slick feel of it as he rubbed it into his pale skin.
Should be liked.
Just dropping a note here
Fyn