The document summarizes how Naughty Dog developed the concept for the infected enemies in The Last of Us. They initially considered an infection that simply killed people, but realized they needed an ongoing threat for gameplay. They were inspired by real-life fungal infections in insects and envisioned a cordyceps-like infection in humans. An artist created a hybrid infected appearance drawing on real diseases and fungi. The studio developed the full biological cycle of the infection, including later stages where the infected's body is consumed by fungal growth. These stages were based on real fungal infections to make the concept believable.

1. Pre-Production
One of the first struggles for NaughtyDog was making world realistic and believable, where
nothing could be seen as a monster. They thought initially of an infection that just kills people, and
the story would be about how humans deal with a post apocalyptic society and how different
people survive.
They then realized that because they are making an action game, a lot of the storytelling happens
on the joystick (through gameplay), and once the infected were taken out, the story could not be
told through gameplay of what happened to their world.
They then brought the infected back in, so when you are fighting the infected you can see the
threat that the people in this world had to deal with and experience it yourself.
An early inception came from a BBC Planet Earth documentary on Cordyceps fungi in ants and
insects, where a fungi infects the insect and takes over their brain. They asked themselves what if
it jumped to humans? How would people in this world react? What would happen to their society?
In terms of appearance they tried out really alienated, sub-human and zombie like concepts but
they needed something more original and believable. One artist made a photo mash up using
images of real life diseases and fungal overgrowth to create a new type of infected. He used the
fungi as focal point for the infected and could be distinguished from a distance with pretty
saturated colours found in other fungi. Elements of it are beautiful, eerily human but very
disturbing. “To us itʼs scarier when things on it are somewhat benign or beautiful”.
The character artist then created a full biological cycle of the infected to show the different stages
of the infection and how it gets worse. They discussed how the infected would move about once
the infection split the face in two, rendering the eyes useless and decided there would be a
ʻclicking phaseʼ where they would use echolocation to navigate with an eery clicking sound.
The last stage of infection is called ʻBloaterʼ, the body is almost fully replaced with fungal plates
and completely takes over the body, and blooms. The body is covered in things that have been
growing on them.
When the infected feels it is going to die it will find a quiet dark corner and becomes part of the
environment, the body is consumed/disappears and the fungi sprouts and spews spores to spread
the infection. These stages are linked to the real life fungal infection, so the player can believe
that this could happen with the science behind it, and they can then get more into the game.
The world is seen as its own character in The Last of Us. They took inspiration from a book called
ʻThe World Without Usʼ which describes in detail how much fighting humans have to do to keep
nature back on a daily basis, and when you stop fighting it, how quickly nature can come back.
NaughtyDog also used previous research on how temples were ruined from the Uncharted series
and put some of those ideas in american cities. They experimented with lots of concept art to
show how the city has changed and how nature has taken over. They also use real life scenarios
such as trees radiating, so the base of a tree isnʼt covered in snow, which makes the environment
more believable and immersive.