I wrote this quite a while ago.

Frank was an unusual skinhead. He didn't hate anyone. But unlike Ferdinand the Bull, Frank knew how to fight. Which was good, because when other young bald men saw him on the street, there was about a 50% chance of violence ensuing.
Neo-nazis hated everyone and SHARPS hated Neo-Nazis. Frank (short for Francis) didn't hate anyone, but he was a skinhead anyway because, to him, it was the only way to grow up white trash and still respect himself.
"They don't own this," he would tell his friends when they asked why he shaved his head, "Rolled-up jeans isn't the uniform of pissants. It's just clothes, and I can wear them if I want."
Which was true, because when nazis or sharps took him to task for dressing like them, Frank could reliably hand their asses back to them humiliated. Unfortunately this meant that Frank had few friends who wanted to be seen with him in public. Chances were high that some thrice-defeated jackanape would emerge from the shadows with an engorged cadre of ne'er-do-wells to seek satisfaction.

He actually hadn't been jumped by skinheads of of any persuasion in awhile. He hadn't noticed yet, but his reputation in those circles as someone whom it is unwise to trouble had become street-knowledge.
He hadn't noticed the drop in skinhead antagonism because he still found himself fighting with some regularity.
Something else about Frank was that he had a penchant and no small skill with spray-can graffiti. He'd been designing and refining tags since he was a child in middle-school. Some of the prettiest burners in town (in his opinion) were his. While he'd been practicing for years, he'd only recently begun writing in the streets where anyone could see it. His reputation amongst other graffiti writers as a formidable combatant was not yet well known. He often found himself challenged by some spray-can veteran taking it upon himself to haze Frank as a newcomer.

Frank got the impression from the other skinheads he'd met that he was perhaps the only one who had an appreciation of the '50s and '60s New York jazz scene, so that was another thing that made him unusual. But none of these are the most unusual thing about Frank.
Frank was alive during one of the human race's most historically significant moments (but so were millions of other people, so it's not that special).

At the moment Frank was cruising a main street with no real distination but food, and listening to Herbie Hancock contemplate the amusing fact that life goes on.
A week ago Frank had been in this area of town and heard a scream. At least, he thought he'd heard it. As several newspapers had pointed out, it was amazing he'd heard anything, being several blocks away. But he must have heard something, because he pinned the accelerator to the floor of his stale yellow pinto for three blocks the wrong way up a one way street. He arrived at the wide-open downtown plaza and came to a screeching, dragging halt in time to see what had at first seemed like some kind of strange bear, about to kill someone lying on the ground before it.
Frank was aware of his thoughts only now, in retrospect. Seeing such a large and vicious creature, he had assumed that someone, help, must be on the way. There were a few observers, one of them must have a cell-phone. One of the people he'd seen fleeing would probably call the police.
So Frank had been under the assumption that all the poor man on the ground needed was time. Time for people with equipment to show up and do whatever. Frank was not, however, totally cognizantly aware of this assumption. He was running across the bricks as fast as he could, as the great hairless beast (it was hairless he could see as he got closer) reared and dropped, claws much too large for a bear falling toward the helpless man.
Frank was near enough now, and as the claws fell his moment to jump had come, but jump and do what? Some part of his mind developed the seed of a thought which unfolded only now, a week later in his car, that it was amazing how many thoughts the brain was capable of processing in an instant. For example, the choice of what to do with his momentum and how best to serve the soon-to-be-dead guy. Jump on the monster? He could see now that there was no other word for it. Jump in front of the guy on the ground? No, then they'd both die. The only reasonable thing to do was hurl himself at, and he did.

Running at top speed, Frank leapt without hesitation and grappled the huge arm, wrapping his arms around it and throwing his legs out in front. It was barely enough force to avert the strike, and claws struck the bricks next to the cowering man's head. A few bits of brick flew from the point of impact.
Still gripping the great ugly claw and lacking a new plan, Frank held on tight and felt its muscles move beneath the skin. They tensed, he tensed. The creature moved to strike at Frank with its left arm, but drew its right arm out harm's way and in so doing whipped Frank to safety as well. Reaching the end of the arm's motion, Frank felt his weight pull at him and he was nearly shaken loose. The man on the ground scrambled to safety, and Frank wished he too could get away. But he knew if he were thrown, it would take the rest of his lifespan to get to his feet.
Maybe it was a bull? It had huge horns, pointed and rough-looking. It looked as though it could have been a bull if it would quit standing on its hind legs like a bear.
It stood and tried to examine Frank by holding him up in front of its face. Frank's legs swung, a little like a ragdoll, around behind the monster's head. Eagerly he seized the opportunity to keep the arm in its disadvantageous extended position. He locked his legs around the monster's left horn and pulled, demanding of himself more strength than he thought he had.
The combination of surprise and leverage must have worked, because though it struggled against him, Frank was able to pull the huge arm into a sort of upside-down version of a police arm-lock, its elbow pointing to the sky.
The monster made a very loud, very unpleasant sound and Frank held the arm, hanging now upside-down from the creature's horn. Straining against colossal bone, muscle and tendon, he straightened his back as much as he could, pulling the badly twisted forearm down its back toward the ground.
The monster spun 'round to try and grab at Frank with its good arm, but lost its balance and landed awkwardly on its contorted shoulder which, with the tension of Frank's arm-lock, dislocated. The convulsion of pain which shook the monster's body finally threw Frank to the ground several feet away.

Though it was night, the plaza was well-lit, and Frank could see the monster's eyes. They had no animal fear. They were frighteningly hateful eyes. Even the people who picked fights with Frank had something else in their eyes. Confusion, anger. But these large , vicious eyes help only contempt.
Frank had landed near a trash can. He'd planned to run if he got the chance. He had that chance now, but seeing the eyes compelled him to a different course of action. He wanted to run and be safe from the thing. Having seen its eyes, fleeing no longer seemed safe. Frank grabbed a bottle from the top of the garbage piling out of the can, broke it on the concrete cylinder which held the receptacle in place, and charged at the beast hoping to reach it before it recovered. He was focused on its eye. If there was any shot at hurting this great awul thing, it had to be those hateful eyes.
Running towards the creature again, and again using his momentum, he struck the jagged glass at the monster's eye, hoping the eye-socket was big enough to let the bottle in. It wasn't, and the glass shattered apart lodging wedges of it in both the monster's face and eye, and Frank's arm.
Ignoring the pain shooting through his arm, Frank immediately shoved his hand into the blood and glass that now filled the eye socket. He made a claw of his hand as the monster screamed. With his free hand he grabbed the monster's right horn, the one closest to him, and pulled. Like pulling taffy, the eye came out, and again without hesitation Frank shoved his arm back into the eye socket, shoving past blood, glass, torn tissue, and into soft brain, made tough by its confinement in the skull.
Distantly noting his lack of a gag response, Frank thrust from the shoulder, working his fingers into what felt like wet dough. The creature was still moving, but not thrashing now. It was twitching in futility, with Frank's hand in its brain. He was wiggling his hand as much as he could, trying to cause as much tissue damage as possible. It stopped moving. Frank kept tearing at it's brain. It stopped breathing. Finally Frank relaxed.
When he looked around, his arm now stuck in the beast's head up to the elbow, he saw the crowd now included stunned police officers and firefighters. With effort he removed his arm from the socket and it spewed gore like uncorking a barrel of thick vomit.
Frank puked. The rescue workers whisked him away to wrap him in blankets and give him coffee like they do on television. They removed the glass and bandaged his arm.

In the week following, he'd given his accountof the event in several interviews and had learned that no one seemed to know what the animal was or where it had come from. Before Frank arrived, the witnesses at the plaza said that the monster appeared without anyone seeing it approach. It was just there, in the middle of a crowded downtown area, and it attacked the nearest person, the man Frank saved.
The weird thing, to Frank, wasn't that it had happened in the first place. Extraordinary things happen to people, it's just a fact. But that life has no choice but to continue on afterward regardless. Here he was, Francis Hunter: Monster Slayer, driving down the street like anyone else. Hungry like anyone else. Not that he wanted to be famous. Not that he was dissatisfied with it. But he thought it was kind of funny that something so life-changing could happen to you, and then it doesn't change your life.

This late at night there were few dining options. Of the three, one didn't have a reputation for cockroaches. It was also the more expensive of the three. By small margin, but enough for Frank to feel like justifying his choice.
Frank had worked at a grocery store until earlier this day, when he'd been informed of his termination for shoplifting. He suspected the real reason was that his superviser was afraid of him. Now moreso since Frank had been featured on the news for his heroic act of violence. Allowing himself a moment to indulge in petty crap, he mentally acknowledged the fact that his supervisor lifted things from the store with nearly every shift.
Then the light turned green. Frank used red lights as therapy. Until it turned green, he was free to engage the fuckers at their own level, with all the petty drama and narrowminded backstabbing he'd come to expect from his fellow working stiffs. And when the light was green, he left all the stupid vitriolic shit there at the intersection to get run over into the ground by every following car, while he drove away from it a free man.

When he arrived at the 24-hour café, Frank found it more populous than he'd expected. Several tables had been relocated to make room for the lyrical stylings of some minor local celebrity. This happened often, and sometimes Frank found it enjoyable. But tonight he wanted a seat and a table.
Fortunately, one fan didn't mind sharing his table. Frank opened his black sketchbook and laid it on the table after ordering. He uncapped his pen and studied his latest design. It was for a mid-sized throw-up tag, and it wasn't satisfying him. He'd hoped to channel some aggression into creativity. But instead of angry, the thought of last week's monster kept popping to mind, and Frank's amotional response to this was mostly awe. Not respectful awe, but more like confused wonder. The kind of feeling one associates with the phrase "what the fuck."

From my notebook.

I had a dream.
Soldiers were deployed - urban ruins, there were monsters, sort of - a disease which controlled its host, a vicious hunter without a body. The victims become the predators - the soldiers' company is trying to get to safety, but they've suffered losses, the most recent of whom is stalking them from the shadows like Gollum, waiting to get the upper hand, behaving like a hyena or some other cautious but feral scavenger/hunter, like a wild dog. The company's progress is slow because they have with them a partially infected soldier - he sleeps to keep the parasite dormant - it gives him superhuman abilities like other victims, but for some special reason, some unique circumstance owing to blind luck, the infection's control over his mind is weak(er). When he wakes up he can smell the other infected hosts and can hunt them with the strengths granted him by the parasite, but the more physically active he is, the more the parasite consumes his body in its ongoing bid to control it.
Other victims' bodies are attacked only until the brain's control is wrested. This special soldier's brain has remained in charge, perhaps only because the parasites have not yet had success with the brain, for whatever random fluke of biology and genetics.

So the squad's captain or whatever finally decides to wake up the sleeping guy because they've been cornered in this one room of a bombed-out building - formerly a stair-well from the looks of it.
The infected soldier has chosen this opportunity to take shots at the squad, company, whatever. I guess it's small, so that's like a squad, right? About 5 guys now (men and women, actually) 7 or eight originally (when they set out, before the dream takes place).
The soldier wakes up as little as he can to defend the team. He tries to snipe the infected with his sidearm, his pistol, without opening his eyes all the way or focusing his mind on the task.
When that proves impossible, he grudgingly wakes up more, and gets up off the stretcher they've been carrying him on. (His pistol ran out of bullets.) Still refusing to fully direct his mind to a focused task, he tries to keep his mind relaxed and as close to unconscious as possible while still carrying out his task. Dreamily, he leaps to the broken-off balcony of the second floor without the aid of the stairs [which were rubble anyway].
Quickly, and without thinking (mostly) he draws his bootknife and charges the startled infected soldier [who had backed around the corner of the stairwell door into the remnant of a second-floor hallway, which was about 20 ft. long and ended in a T-intersection which was broken off on both sides, letting sunlight in from the dim, gray sky], tackling her to the corner where the wall meets the floor. [at the intersection where the other hall would cross it if there were another hall. They were both half illuminated. The sky looked like it could rain at any moment.]
Her expression is feral, but startled - her eyes look distant - she has a blonde miitary crew-cut, I think.
The special soldier relaxes most of his body the instant he makes the tackle, both to get ready to fall back asleep more easily, as well as to use his dead weight to incapacitate the infected one. Not that that's necessary - as soon as they hit the floor, he pressed his knife blade into her throat.
Her wild, frightened look relaxes into a peaceful, present look, as the parasites flee her dying body, releasing her from their control. She smiles and closes her eyes as blood begins to flow out her mouth and neck.

The was the end of the dream [this is still from what I wrote when I woke up].
A note; for the special soldier, trying to hunt and kill without waking up felt similar to the feeling of trying to record a dream, that same attempt to loosely organize thoughts and actions without shifting your awareness completely over to the waking world, or else you'll be unable to summon the sleep-thoughts which are vital to the process.

Other notes: Parasites could be alien - no inherent mechanism for seeking the brain. Wouldn't have to be alien for that though. Sort of like sperm bombarding until one makes it - the parasites swarm destruction through the body until some find the control center, at which point it sends signals throughout the appropriated channels which are conveyed to the other attacking parasites, calming them and eventually converting them for other uses to the ... colony. Such as breeding and ability enhancement (pain dulling, allowing greater feats of strength and endurance, to the dentriment of the host's muscle fibers, which the parasites attempt to patch up in a makeshift sort of way - possibly using themselves as replacements for destroyed fibers, also enhancing the receptivity, signal strength and nervous response time of the sensory organs - etc.)
It can be contracted from close proximity to a dying infected host though this is a lower risk, since most of the fleeing parasitic microbodies will already have been converted from Stage 1 invaders by the control signal into their various more specialized roles. Only the controllers are a real threat (though the others may attach themselves to a nearby viable host, if the genetic conditions are similar enough, without the controllers they will do nothing), and even then only if genetic factors are similar enough for the now-specialized microbodies to find something they can keep a hold on.
The real threat of infection comes from being near an infected host during Stage 3, when the specialized breeding mircobodies are manufacutring millions of non-specialized Stage 1 invasion microbodies.
During Stage 3 a host is a cloud of infectious death - this cloud could make them unreasonably difficult to combat - if I wanted to scale it back I could say that the approproation of so many of the body's resources during Stage 3 makes the host body sluggish, lethargic, or even catatonic. No such detail was provided by my dream, but that would make things a little more manageable.
Stage 3 could be cyclical (my first inclination) or it could mark the end of the parasites' destructive lifespan. No detail was given about this either, though I think cyclical makes the most sense. It feels more right. The bit about immobility during the high-contagion phase seems purely down to my preference. Maybe immobile, followed by a surprising change toward the ambulatory.
I don't know why they would be violent or semi-intelligent though, that's just how the dream had it.