• Just the general idea of "severance". If you're selected for the implant procedure, they drill a hole in your head, and pretty deep too for easy access to the brain. Then, they stick a needle through that hole, and, the device is implemented. Upon certain conditions, the device then turns you from your "outie" to your "innie". And they are two completely different people. For instance, your innie may be the nicest person to hang out with, but their outie is cold. Lumon's business is so confidential that some employees need to be different people so that their true goal is uncompromised.
• The more the show goes on, the more it's made apparent that Lumon is run very similarly to a cult, particularly with their worship of Kier Eagan, the company's founder, who's treated like a divine prophet by both severed and unsevered employees. The Company Town where most scenes in the outside world take place is also named after him, with the license plates for the unnamed state where it's located having his face on them, and Ms. Cobel's aunt Sissy is a particularly fervent worshiper. Just how much influence does Lumon's cult-like practices have?
• The Billie Holiday cover of "I'll Be Seeing You," which is the Leitmotif for Mark's (and eventually Gemma's) grief and loneliness, is extremely unsettling and provokes intense unease whenever it plays.

• In the second episode, we're treated to a shot of Helly's head being cut open as part of the severance implant procedure. Ugh.
• The punishments in the Break Room, where innies who act out are tortured:
  • Petey plays a recording of an audibly upset Mark reciting the dictated creepy apology.
  • Later, Helly is forced to recite the apology over 1,000 times while a bright light is shone in her face.
  • After one visit to the Break Room, Outie Mark checks out of work with his knuckles visibly reddened from a punishment. Lumon told him that he caught them while moving a water cooler bottle.
  • Helly and Dylan muse over the low voice they both heard. Dylan hears a baby crying revealed to be his son and Helly hears her father.
• Helly's method of resigning which her outie cannot ignore: hanging herself in the elevator, so her outie reawakens mid-suicide attempt. Mark is visibly traumatised just witnessing it, and Helly has visible skin abrasions from it for the rest of Series 1.
• Helly's entire situation this season is one. Like all of the main innies, through no fault of her own, she's essentially born just to do her job, her whole life is in some creepy white void maze staring at a screen, from her perspective she literally has no break from her job, clocking out one day and immediately waking up the next, but also her outer self is actively refusing to let her escape this hell. Refusing any attempt to quit, declaring her not to be a person, and even going right back to work as soon as she was recovered after Helly forced her to experience what was essentially a murder-suicide attempt.
• It is revealed that Gabby Arteta used severance in order to avoid remembering the pain of childbirth. Which means that there is an alternate version of her buried in her mind, which was building her own plans for her son, underwent the agony, and was then turned off like a switch instead of raising her child.
• Turns out a waffle party is getting to watch a bunch of strangers in masks and lingerie yanked straight from the Uncanny Valley do a creepy dance in an insanely dark room in Kier Eagan's house... after eating waffles. This takes the cake for the most surreal moment in an already surreal show.
• Devon finds out that Mark's boss Cobel and Mrs. Selvig are the same person, after she had given Eleanor to her to watch before going off to speak with Mark. And now her and the baby are nowhere to be found. It turns out Cobel left her behind before heading back to Lumon, but before then Devon is a frantic mess trying to find her child.

• The Innies learn that the Severed Program is far broader than they realized, with a corporate video saying that severed facilities exist in 206 countries around the world.
• Irving’s dream during the ORTBO features Woe, one of the Four Tempers of Kier, portrayed as a zombie bride.
• Irving, deducing that Helly's outie has masqueraded as her since they returned, dunks her head in an icy river until she confesses and Milchick switches her back. Helly awakens to her friend attempting to drown her (though Irving apologizes and comforts her), having no clue where she’s at, and with the others having learned she's an Eagan before she can explain.
• Helena's situation is awful; despite her reluctance to return to the severed floor where she's nearly died twice, she's pressured into returning while knowing that Helly in her body is a means to keep Mark happy.
• Gemma's fate in the floor beneath the severed floor. Every day, she enters a handful of rooms, and each room causes a different, unique Innie to activate. Each Innie is subjected to their own personal torment nexus, from knowing nothing but painful dental checkups to perpetually being on a simulated plane going through extreme turbulence about to crash, to being forced to hand-write hundreds of thank-you notes, something we learn that episode Gemma hated doing. Gemma only feels the physical effects of each one afterwards (hand cramps, mouth soreness) but not the emotional distress. Gemma is not just in hell, she is in several dozen hells simultaneously. As awful as Ms. Casey has it, she arguably is suffering the least of any of Gemma's dozens, possibly hundreds of Innies.
  • It's somehow even worse than that: the person who runs said hells is a Mad Doctor with a creepy crush on her who abuses his power by doing things like pressuring one of the Innies to say that she loves him and specifically lying to her about Mark remarrying and having a daughter.
  • The season finale implies that the point of the experiments on Gemma is to test whether there is any bleedthrough of negative emotions past "severance barriers". While everything we have seen previously is causing suffering to innies while the outie remains ignorant, the final Cold Harbor scenario flips it on its head: Her innie is given the task of dismantling a baby crib, obviously calling back to the flashbacks where Mark bought them a self-assembled crib, to see whether her outie's experiences with her infertility will cause any reaction in her innie.
• The machinations involved in Gemma's abduction and enslavement.
  • As noted elsewhere, it's implied that she may have been on their radar since the blood drive where she and Mark met.
  • Then, after her miscarriage, she goes to a fertility clinic that may also be associated with Lumon...
  • ...Which raises the question of whether her miscarriage was an accident, or whether Lumon sabotaged her pregnancy to get her into the clinic...
  • ...Which leads to the "personality test" and the Chikhai Bardo card she gets in the mail...
  • ...Which is the same card that Dylan stole from the production floor in O & D, back in season 1...
  • ...Which suggests that they've pulled this maneuver on many, many people before now.
  • Moreover, Gemma says that the card depicts "one guy fighting himself" as a representation of "ego death." What if she wasn't abducted forcibly? What if she was somehow manipulated into going with them willingly?
• Miss Huang's banishment to Svalbard is just straight-up abuse. Whatever else you might say about her, she is still a child, and Milchick separates her from her parents and sends her to fend for herself in an Arctic wasteland as punishment for challenging him.

Cold Harbor

• Seeing both Mark as an innie and outie try to convince each other of their own goals is pretty distressing, especially since the seeds of discord are sewn as the conversation progresses. The outie is doing everything he can to convince his innie that Gemma needs to be saved for both their and her sake, but the innie gradually gets more antagonistic. Even the outie revealing the reintegration process isn't enough to sway the innie. The conversation concludes with Innie!Mark explicitly saying that the next time he wakes up, and he's not in Lumon, he's going to make sure his outie will never see Gemma again.
  • Even worse? Innie!Mark chooses to free Gemma, but simply tags along with Helly to secure their future. His innie has grown such contempt for his outie that he doesn't see the bigger picture, and is more than willing to remain in control so long as it benefits him and by extension Helly. It's All About Me rolled into Grand Theft Me...
  • Also, not only are letting Gemma go and running away from Lumon's control pivotal moments in the show, but as mentioned in the Recap page, they are poised to be Lumon's "biggest enemies". Who isn't to say that this little stunt could be the catalyst for turning off the Severance program in the future?
• When Mark returns to Lumon, he is greeted by a massive painting that depicts him, the Macrodata Refinement team, some Lumon higher-ups, and the Eagan family looking at him with pleasure. It's Mark finishing Cold Harbor, meant to be Lumon's finest hour, and easily the most uncanny painting in the series by far.
• There have been gags referencing what type of data they've been refining, but The Reveal turns those jokes into a Cerebus Retcon. Every single file they've been refining? They are all of Gemma's various innies. And that's not all. Once Cold Harbor is complete, Gemma will be disposed of, and the Macrodata Refinement team will be disbanded for good, Lumon no longer seeing use for them. You Have Outlived Your Usefulness doesn't even begin to describe it.
  • And, all of the negative feelings they feel when they find certain numbers? Those are all feelings of woe, dread, malice, and frolic. You did not read that wrong, MDR has been taming Gemma's four tempers all this time. And what's the end result for her? Basically turning her into an Empty Shell devoid of negative feelings, with a mindset open to subjugation and doing their horrible bidding without emotion or hesitation.
• Mr. Drummond once he has Mark at his mercy and is strangling the life out of him. In wide closeups we see how he growls and snarls and bares his teeth like he's not so much a human being but an attack dog wearing a human skin.
• Conversely, even though he absolutely deserved it, there’s the rather abrupt way Mr. Drummond dies. As Innie!Mark is riding the elevator with Drummond, bolt gun shoved into his neck, he explains how he wants him to take him to where Gemma is being held once he switches to his Outie... but he winds up getting cut off by his body locking up during the switch over. And then he pulls the trigger on reflex. As such, the very first thing Outie!Mark is made cognizant of is Mr. Drummond violently bleeding out all over him, and then collapsing through the elevator door.