Not much is known about them other than that they are psychopaths. They seem to constantly talk about indulging to their desire of murdering Miles and possibly eating his tongue and liver. They seem to be obedient to Father Martin, the reason for this is unknown.
The Twins both appear to be very calm and intelligent when compared to other inmates within the asylum and have some semblance of humanity left in them, for instance they can open and close doors rather than mindlessly bash them down like other variants. Neither of them wear any clothing whatsoever. They seem to prefer ambushing targets in long corridors, using their numbers to flank Miles. They are silent killers, and therefore do not run or talk when chasing Miles, they walk calmly rather than sprinting and prefer to kill their victims in silence. Their weapons of choice seem to be only iron machete-like blades. Unlike the other Variants that roam the asylum, getting too close to either of them will result in instantaneous death rather than getting hit and taking damage. In addition to staying quiet, the absence of noisy accessories and appendages makes it incredibly difficult to locate their exact location without running into them, requiring the player to stay more vigilant and observant than with other Variants.
Miles' first encounter with them is at the beginning of the Prison Block, where they discuss killing Miles and taking his tongue and liver, but deciding not to do so yet, for it would be impolite towards Martin Archimbaud, who told them not to touch Miles. They become hostile later on when they've decided they had enough patience with Miles, despite Father Martin's wishes. They are encountered once more near the prison showers, where they manage to trap Miles in a narrow corridor and he is forced to use the smashed window to evade them. Further encounters include the Female Ward where they lie in wait behind a large door near two hallways and when Miles returns to the Administration Block in the theater room. They cease being hostile once Miles reaches the Chapel during Father Martin's crucifixion.
The Twins make a brief cameo in the Recreation Area. They are seen walking to either side of Waylon at one point, mentioning that he looks nervous and they would like to kill him. Once Waylon loops around to the basketball court, they cease hostility and wait in front of the designated door. They will not attack unless Waylon gets too close. They return to antagonizing Waylon as he hurries to escape the basketball court, after he climbs up the ladder, they are not seen again. It's assumed they headed back to the Prison Block, where they will encounter Miles Upshur for the first time.
The Twins speak in incredibly calm tones, never raising their voices, and speak casually about everything. However, they seem to be murderous cannibals, as they usually talk about cutting Miles open and eating parts of his body such as his liver and tongue. They have what is almost a hive mind, having the same thoughts and same psychopathic personalities, talking in choppy sentences and sometimes finishing each other's. They are devoted to Father Martin, making it likely that their insanity bleeds into believing The Walrider religion, and simply walk when chasing Miles instead of running. This, combined with their lack of clothing and never speaking while chasing Miles, makes them almost completely undetectable and silent. They are also cynical, as evidenced by their deadpan use of sarcasm once they see Miles "disappear".
Both twins are pale, muscular, and hairy middle-aged men who completely lack any clothing, are slightly drenched in blood and dirt, and have scars on the sides of their stomachs, making it likely they were conjoined before splitting up. The first twin has a hump-shaped head with a neutral face and missing teeth, having brown hair everywhere but the top of his head. The second looks much the same but has a sterner face and messy dark brown hair covering his entire head. Despite being Variants, they lack any deformities caused by the Morphogenic Engine whatsoever, but their repulsive features suggest they are inbred.
- In the second demo version, their appearance is slightly different. They resemble other mental patients more than having their unique look, as well as appearing fully clothed. In both versions they have machetes and can kill Miles.
- When the shorter twin breaks into the theater, he is seen holding a cleaver instead of his usual weapon, the machete.
- The pre-updated version of the game had the taller twin guarding a door next to the elevator in Return to the Administration Block chapter.
- In the game's files, they are both referred to as "Duponts". This is likely a reference to The Adventures of Tintin, as two characters in the stories are named "Dupont" and "Dupond", who behave similarly, and look identical.
- They are never mentioned throughout the game despite the numerous encounters and are two of the four characters who were never addressed with a proper name. The other two being Stephenson and Pyro. They are referred to as "The Twins" in one of the Red Barrels' official game art.
- They could have possibly been conjoined twins, considering that they each have an identical scar on their stomach. The shorter twin has it on the left side of his stomach, while the taller twin has it on the right side of his stomach. Though this theory could be dismissed considering their possible age difference and could simply be a residual scarring from the experimentation conducted on them.
- The twins' character models are based on Roger Ballen's portrait photo of (possibly inbred or victims of the fragile X syndrome) twins Dresie and Casie, photographed in West Transvaal, South Africa in 1993.