You’ve heard that clicking sound. If you’ve played the games or watched the HBO show, that rhythmic, guttural snapping is enough to make your skin crawl. It’s the sound of a world that ended not with a nuclear bang, but with a fungal whimper. The Cordyceps Brain Infection (CBI) isn't just a plot device; it’s a terrifyingly grounded take on biology gone wrong. Honestly, what makes the types of infected in The Last of Us so much scarier than your average zombie is the timeline.
This isn't just "dead people walking." It’s a progressive, agonizing evolution.
The fungus needs the host alive, at least at first. It wraps itself around the brain, rewiring instincts and turning a regular person into a frantic, aggressive vector for spores. Most people think of them as one big group of monsters, but the nuance is where the real horror lives. Depending on how long that fungus has been "cooking" inside a human skull, you get something completely different. From the sprinting terror of a Runner to the hulking, armor-plated nightmare of a Bloater, the stages of infection tell a story of total biological takeover.
The Early Days: Runners and the Loss of Self
It starts fast. Within 24 to 48 hours of a bite or breathing in enough spores, the host loses their mind. We call these Runners. They’re the first stage. They look almost human, which is probably the most disturbing part. You can still see the person they used to be—sometimes they’re even wearing a flannel shirt or a watch.
But they’re fast. Really fast.
Unlike the slow, lumbering zombies from old George Romero movies, Runners have all the physical capabilities of a living human, just without the moral compass or the pain receptors. They hunt in packs. They moan. Sometimes they even sound like they’re crying or whimpering when they aren't actively trying to rip your throat out. This stage is all about speed and numbers. They haven't lost their sight yet. Their eyes are usually bloodshot and unfocused, but they can see you from across a parking lot.
If you're playing the game, you know the drill: stay low, move quiet. If one sees you, they all see you. It’s a chaotic mess of flailing limbs and screaming. What’s interesting—and kinda tragic—is that Naughty Dog designers have mentioned that Runners sometimes resist the urge to attack, but the fungus wins every time. It’s a puppet master situation.
Stage Two: The Stalker’s Patient Game
Wait a few weeks, maybe a few months. The fungus starts growing out of the head. It begins to obscure the face. This is stage two: Stalkers.
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Most players hate Stalkers the most. Why? Because they’re smart. Well, "fungal smart." While Runners just charge at you like a linebacker, Stalkers will literally hide behind a doorway and wait for you to pass. They’ve lost some of their vision, but they’ve gained a primitive form of echolocation. They’re the middle ground between the frantic energy of a Runner and the calculated blindness of a Clicker.
They stick to walls. The fungus starts to bond with the environment, meaning if a Stalker stays still long enough, they basically become part of the wallpaper. It’s a jump-scare waiting to happen. In the games, particularly The Last of Us Part II, the Stalker encounters in the office buildings are legendary for being pure nightmare fuel. You don't hear them coming. You just feel them.
The Icon of the Apocalypse: What Makes Clickers So Famous?
After about a year of infection, the host's face is completely gone. Split open. Replaced by a hardened, blooming fungal growth that looks like a twisted cauliflower. These are Clickers.
They are the most famous types of infected in The Last of Us for a reason. They can't see a thing. Total blindness. But their hearing is tuned to a terrifying degree. They use echolocation—that clicking sound—to "see" their surroundings by bouncing sound waves off the walls and, unfortunately, your face.
Clickers are significantly stronger than humans. You can't just punch your way out of a Clicker's grip; in the game’s mechanics, if they grab you and you don't have a shiv or a weapon, it’s game over. It’s a one-shot kill.
There’s a weird beauty to them, in a morbid way. The practical effects team for the HBO series spent months getting the "bloom" right. It’s not just a mask; it’s supposed to look like a biological explosion. They represent the point of no return. The human host is essentially a passenger in a suit of fungal armor.
The Heavy Hitters: Bloaters and Shamblers
If an infected person survives for years—usually in a damp, dark environment—they become a Bloater. These things are massive. They’re slow, sure, but they’re covered in thick, calcified fungal plates that act like natural Kevlar. You can shoot a Bloater with a pistol all day and it’ll just keep coming.
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Bloaters don't just bite. They throw.
Specifically, they rip pouches of mycotoxin spores off their own bodies and hurl them like grenades. If you breathe that stuff in or get it on your skin, it’s a bad time. Then there are Shamblers, which showed up in the Seattle setting of the second game. They’re similar to Bloaters but instead of throwing things, they just emit a constant cloud of acidic spores. When they die, they explode. It’s a final "screw you" from the fungus.
These stages show the Cordyceps’ ability to adapt to the environment. In the humid, rainy climate of the Pacific Northwest, the fungus evolved differently than it did in the dry heat of the outskirts of Boston. It’s a reminder that this isn't a static virus. It’s a living, breathing ecosystem.
The Rat King: An Evolutionary Freak Accident
We have to talk about the basement of the hospital in Seattle.
The Rat King isn't a "type" of infected in the traditional sense. It’s an anomaly. It is a mass of multiple infected—Runners, Stalkers, and a Bloater—that have been fused together by decades of fungal growth in a confined space. It’s a super-organism.
It’s the ultimate nightmare of the Cordyceps. It shows that the fungus doesn't just want to spread; it wants to merge. It’s a singular, thrashing pile of flesh and spores that can tear apart into smaller, individual monsters if you damage it enough. This thing represents the absolute extreme of what twenty years of infection can do when left undisturbed.
Why the Biology Matters
Most zombie media relies on "magic" or hand-wavy science. The Last of Us uses real-world inspiration. Ophiocordyceps unilateralis is a real fungus that infects ants, takes over their motor functions, and forces them to climb to a high point before bursting out of their heads to spread spores.
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The game just asks: "What if it jumped to humans?"
This grounding is why the different stages matter. It’s not just about variety for the sake of gameplay; it’s about a lifecycle. You aren't just fighting monsters; you’re fighting a biological process that is slowly turning the human race into fertilizer.
Survival Realities: How to Handle Each Stage
If you actually found yourself in this world, the rules for survival change based on what you’re looking at. You don't treat a Runner like a Clicker.
- For Runners: Keep your distance. They are clumsy and prone to rushing. Use the environment to bottle-neck them.
- For Stalkers: Check your corners. Seriously. If it feels too quiet, there’s probably one behind you. Don't wait for them to move; flush them out with a bottle or a brick.
- For Clickers: Stealth is your only real friend. If you have to fight, use high-caliber rounds or fire. Fire is the great equalizer in this universe. Cordyceps hates heat.
- For the Big Guys: Don't be a hero. If you see a Bloater and you don't have a flamethrower or a pipe bomb, just go the other way. There is no shame in living to see tomorrow.
The biggest mistake people make is assuming they can handle a group the same way they handle a lone infected. The synergy between these types is what gets you killed. A Clicker flushes you out of cover with sound, and a Runner catches you while you’re scrambling.
Moving Forward in a Cordyceps World
Understanding the types of infected in The Last of Us is about more than just knowing what to shoot. It’s about recognizing the stages of a decaying world. Every Clicker you see was once a person who probably thought they could survive the first week. Every Bloater is a testament to two decades of terrifying resilience.
If you’re looking to dive deeper into this world, pay attention to the environmental storytelling. Read the notes left behind in the games. You’ll find stories of people watching their loved ones go from the "twitching" phase of a Runner to the "blank stare" of a Stalker.
The next time you hear that clicking sound in the dark, remember: it’s not just a monster. It’s a biological success story. And you’re just the next potential host.
Pro-tip for your next playthrough: Focus on upgrading your "Listen Mode" range and stealth speed first. Knowing exactly which stage of infection is behind a wall before you open the door is the difference between a successful scavenge and a very messy death. Gear up, stay quiet, and always keep a brick handy. You’re gonna need it.