[Warning: Spoilers for The Last of Us: Part 2 below]
Throughout The Last Of Us: Part 2, the Seraphites (also known as "Scars") are a consistent threat to both Ellie and Abby on their adventures. In much of the game's early trailers and gameplay demonstrations, the Seraphites were shown to be a dominant and brutal force in post-apocalyptic Seattle. While the Seraphites are a looming threat in Ellie's story, they are thoroughly explored in Abby's part of the game as she teams with Yara and Lev, who both used to be part of the organization.
The Seraphites alone are quite an interesting group to analyze in Ellie and Abby's adventure. However, many players seem to have glossed over another potentially more deadly organization in the narrative. The Rattlers are introduced late into the game in Santa Barbara. Although the player only spends a few hours in this final act, The Rattlers seem to behave much differently than the Seraphites. Rather than killing in the name of an ideology, it seems their motive is to enslave people to work on farms. If captured victims fail to comply, the consequences are deadly.
Although the Santa Barbara section of The Last Of Us: Part 2 is only a few hours long, Naughty Dog was very careful to sprinkle in clues as to who the Rattlers are. The player's first exposure to the Rattlers in gameplay is when Abby and Lev discover a strange work of graffiti on a house. Lev notes it may be the Fireflies, but Abby notes this symbol looks nothing like it. Also, if the player is thorough enough, they find that one of the houses in the area has a letter from a victim of the Rattlers, and it is discovered he took his own life in fear that the group will find him.
Soon after Abby and Lev reach contact with the Fireflies through the hidden radio, they are ambushed by the Rattlers. One of them notes Abby's muscular build being of importance to them. After this point, the player never gets to control Abby again. Once Ellie becomes the focus of the narrative for the final time, she is soon caught by the Rattlers, but manages to escape while also collecting Abby's whereabouts. In the journey to the Rattlers base, players find out The Rattlers enslave people and name anyone who tries to escape a "stray." It is suggested that unthinkable torture befalls any who attempt to achieve their freedom. The player is shown that they have many infected tied up on chains around the farm, and one of the Rattlers refers to an infected as "Anthony," presumably the infected human's name. It seems highly likely that this chaining and exposure to the infection is a punishment for those who have failed escape.
This within itself is horrifying and inhuman, even for The Last Of Us Part 2. However, once Ellie reaches the cell where Abby is supposed to be held, the prisoners tell Ellie she is down by the beach. What Ellie finds is the remnants of what was once a strong and determined woman. Abby and Lev have both been pinned up and tortured by the Rattlers. Ellie cuts her down, and soon after the two fight for the last time in the game, but Abby is undeniably physically damaged and the strength she once had has been completely lost. Seeing Abby so broken down by the end of The Last of Us: Part 2 is not only a terrifying sight, but it also displays the true brutality of the Rattlers.
In The Last Of Us Part 2, the Rattlers aren't given much screen time. Regardless, their disgusting routine of torturing and enslaving people is an unsettling event to witness. It is rumored that originally, the Santa Barbara portion of the game was supposed to be much longer. Despite Ellie and Abby's Santa Barbara venture only being a few hours of a shockingly long game, the prospect of a new undiscovered organization like the Rattlers is exciting to think about if a "The Last of Us: Part 3" ever comes to be.