"Clicker" Language - The Clickers are infected humans who have lost their vision and navigate using echolocation. They communicate in a distinct language that sounds like clicks and chirps, which is actually just the voice actor's attempt to mimic the sound of a dolphin.
Uncharted Board Game - In a few locations throughout the game, players can find a board game called "Uncharted: The Board Game" which is a nod to another popular game series created by Naughty Dog, the studio behind The Last of Us.
Nathan Drake's Ring - The protagonist of Uncharted, Nathan Drake, wears a ring with the Latin phrase "Sic Parvis Magna" inscribed on it, which translates to "Greatness from small beginnings." In The Last of Us, players can find this same ring on a skeleton in one of the game's hidden areas.
Outbreak Day - The Last of Us takes place in a world where a fungal infection has decimated humanity. The game's developers created an "Outbreak Day" holiday to celebrate the game's release and promote awareness of real-world epidemics.
Phone Number - In the game's opening chapter, players can find a phone number on a bulletin board. If they call the number, they'll hear a message from a character in the game.
Naughty Dog Logo - In a few places throughout the game, players can find posters with the Naughty Dog logo on them, which is a nod to the game's developer.
Jak and Daxter Doll - In one of the game's levels, players can find a Jak and Daxter doll, which is a reference to another popular game series created by Naughty Dog.
Firefly Pendant - The Fireflies are a faction of rebels fighting against the game's oppressive government. Players can find a pendant with the Firefly logo on it in a few places throughout the game.
Savage Starlight Comic Books - In several places throughout the game, players can find Savage Starlight comic books, which is a fictional sci-fi comic book series created by the game's developers.
Giraffes - In one of the game's most memorable scenes, players encounter a group of giraffes in a post-apocalyptic city. This scene is meant to be a moment of beauty and wonder amidst the game's bleak and violent world