It’s the sound first. That rhythmic, wet clicking. It doesn't sound like a monster; it sounds like a biological glitch. Most people call them zombies, but if you’ve spent any time with the games or the HBO show, you know that's not quite right. The infected from the last of us aren't undead. They aren't magical. They are very much alive, and that is exactly why they’re so unsettling.
They’re hungry, but not for brains. Their brains are being eaten by something else.
The real-world science of the Cordyceps brain infection
Basically, Naughty Dog didn't just make up a virus. They looked at nature and found something way worse. Ophiocordyceps unilateralis. In the real world, this fungus targets ants. It hijacks their nervous systems, forces them to climb to a high point, and then sprouts a fruiting body out of their skulls to rain spores down on the colony below. It’s a literal mind-control parasite.
In the world of The Last of Us, this fungus jumped to humans. While the game suggests it happened through tainted crops (specifically flour from South America), the horror remains the same. The host is still "in there" somewhere, or at least their body is. They scream while they attack you. They cry. If you listen closely to a Runner—the first stage of infection—you can hear them whimpering between snarls. They aren't making a choice to kill you. Their motor functions have been seized by a fungal growth that just wants to spread.
It's a parasitic takeover. Not a resurrection.
Breaking down the stages of the infected from the last of us
Most games give you one or two types of enemies. Here, the infection is a progressive disease. The longer you're infected, the less human you look, and the more the fungus adapts to its environment.
Runners are the fresh ones. They look like people with a bad flu and bloodshot eyes. They’re fast. They can see you. They’re frantic. You’ll find them in mobs, and honestly, they’re the most "human" part of the nightmare. They still have their sight, which makes them twitchy and unpredictable.
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Then you get Stalkers. These are the worst. Seriously. They have enough fungal growth to start blending into walls, but they’re smart enough to hide. They won’t just run at you. They wait until your back is turned. In The Last of Us Part II, the Stalker sections in the office buildings are legendary for being some of the most stressful gameplay in history because they don't show up on your "Listen Mode" radar if they're standing still.
Clickers are the icons of the franchise. By this point, the fungus has split the skull open. They’re blind. They use echolocation—that clicking sound—to map out the room. If you stay quiet, you're fine. If you knock over a bottle? You’re dead. They’re much stronger than Runners because the fungal plates act like natural armor.
The heavy hitters: Bloaters and Shamblers
Once you hit several years of infection, things get weird. Bloaters are massive, slow, and incredibly tough. They’ve grown thick layers of fungal scales that act like a bomb squad suit. You can’t just headshot a Bloater. You have to burn them. Fire is the only thing that consistently works because it softens that outer shell. They also throw "mycotoxin" spores at you, basically biological grenades.
Shamblers, introduced in the second game, are a variation found in wet environments like Seattle. Instead of physical strength, they focus on gaseous clouds. When they get close, they release a massive burst of acidic spores that burns the skin. And the kicker? When they die, they explode. It’s a final "screw you" from the fungus.
Then there is the Rat King. This isn't a stage of infection. It’s an anomaly. It’s what happens when dozens of infected are trapped in a basement for twenty years and literally fuse together into one giant, multi-limbed mass. It’s the ultimate expression of the Cordyceps' goal: total biological unity.
Why the environment is the real enemy
One thing people often forget about the infected from the last of us is that they don't need to be moving to be dangerous. When an infected person dies in a dark, damp place, they don't just rot. They settle against a wall and become a "fruiting body."
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The fungus grows out of them, spreading across the walls and floors. These areas become filled with airborne spores. In the games, Joel or Ellie have to put on gas masks to survive these zones. If you breathe in those spores, you’re done. It’s a slow, quiet way to lose your humanity. The show changed this to "tendrils"—a subterranean network where if you step on a patch of fungus in one part of town, an entire horde miles away wakes up. Both versions highlight the same thing: the infection is a single, massive organism. It’s a hive mind.
What most people get wrong about the Cordyceps
A common misconception is that the infected are "evil." They aren't. They don't have an agenda. They don't want to rule the world. They are just a biological process. The fungus is trying to survive, just like Joel is. It’s why the story is so tragic.
You aren't fighting monsters from another dimension. You’re fighting your neighbors who had the misfortune of eating the wrong cereal or being in the wrong room at the wrong time. This is also why the "cure" is such a big deal. Because it's a fungal infection, traditional vaccines (which usually target viruses or bacteria) don't really apply. Fungal infections in humans are notoriously hard to treat even in 2026. Antifungals exist, but something that crosses the blood-brain barrier and rewires your neurons? That’s a death sentence.
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Practical survival tactics for dealing with the horde
If you're playing the games for the first time or just want to understand the lore better, you have to change how you think about combat.
- Brick is king. Seriously. A brick is the most versatile tool in the game. You can throw it to distract a Clicker or use it as a melee weapon to save ammo.
- Stealth isn't optional. On higher difficulties like Grounded, you simply do not have the bullets to kill every infected. You have to learn the patrol patterns.
- Bottle the Runners, Burn the Bloaters. Use Molotov cocktails for the big guys. It’s the only way to strip their armor and stop them from charging.
- Check the corners for Stalkers. If a room feels too quiet, it probably isn't. Listen for the faint breathing or the sound of feet on carpet.
The infected from the last of us changed the way we look at post-apocalyptic media. They took a tired trope—the zombie—and grounded it in terrifying, real-world biology. They reminded us that nature doesn't need to be supernatural to be scary. It just needs to be hungry.
To really master the lore, look into the "American Dreams" comic series or the "Left Behind" DLC. They provide much-needed context on how the infection initially crippled the military's response in the early days. Understanding the fungus's lifecycle is the first step toward surviving it, whether you're holding a controller or just watching from the safety of your couch. Stick to the shadows, keep your shivs sharp, and for heaven's sake, stay away from the clicking sounds.