The recording implies that a monkey infected with the Cordyceps bit the man who later recorded the Firefly's Recorder before he died, which probably led to him taking his own life rather than turn into a Runner.
Note: All punctuation and capitalization are typed up as it is heard in the game.
That's four pallets of lab equipment all packed up and ready to go. Now - big question is what do we do with all you guys. They say the tainted batch needs to be put down. You know what I say? I say screw that. Who made a bigger sacrifice than you, right? If anyone deserves to run free out there it's-- Hey, easy. Agh... Shit. Oh no. It bit me. Oh my god...
- Joel: I'm sure glad we didn't mess with them monkeys.
- Ellie: He didn't say where they went.
- Joel: I know. Let's just keep looking.
- Despite the audio showing evidence of infected monkeys, none are seen in the game. Although, it's possible those monkeys were the infected monkeys, because Joel says "Glad we didn't mess with them monkeys". Upon closer examination, one can see that the monkey's eyes are red, the same color as infected humans', while they do not share any behavioral traits. This can be explained by the fact that any given type of Cordyceps fungus only affects one particular species.