Throughout the serving of the menu, everyone was being drugged
Being burned is incredibly painful. Everyone should've been screaming in agony or trying to get away from the flames. We do see a few people cringing and bracing themselves, but no screaming. It's possible that during the serving of the menu, the diners were slowly drugged with something that would reduce the pain. Margot wasn't affected because she hardly ate and drank very little. The staff themselves weren't in agony either and likely took something that was precisely timed to take effect at the final moment; that and a gas explosion that would end it quickly.The "something special" behind the silver door in the restaurant is a full accounting of the menu
In the trivia section, it's stated that the original script had Slowik's head and hands holding the menu behind what is a fire-proof door. In the cottage, which is a replica of the restaurant, the contents of the room behind its silver door is effectively a personal record of Slowik's life and downward spiral. Something quite similar could be inside that room. It could be video of everything that happened recorded through hidden cameras (the script originally had a crew documenting the events), copies of the legally-actionable evidence against Doug Verrick and the techbros, Slowik's correspondence with Tyler, and so forth. Perhaps even final messages from the staff to their loved ones explaining why they chose to die with Slowik—which would explain why no one other than Slowik answered the question of why any of them want to die. It would also completely clear Margot/Erin of any possible legal or civil action, since the authorities and next-of-kin would question why she was the only survivor.It should also be mentioned that when Katherine explains why everyone has to die, she leaves out one fundamental flaw to "The Menu": There wouldn't be anyone to talk about the experience afterward. So, revenge aside, what would be the point? Her ideas and work would never be recognized. It would just be written off as a mysterious tragedy. Leaving some kind of record behind makes sense.
Alternatively, if we put aside the original script, the room behind the door could very well be an exact same replica of the room that Margot found. Rather it's the original, and the room Margot found was the replica. She was very much intended to find that room: from Elsa priming her when she asked about the first door. But what in that room was actually authentic in terms of uniqueness? We learn that the radio is a sham, and the photos and newspaper clippings, while revealing, are entirely replicable pieces of Slowik's past.If the restaurant is already an exact duplicate to reflect Slowik's obsession, why not have a hidden room be the exact duplicate as well? Whichever door Margot went through, she would've fallen into the same trap.
It's not about killing the guests, it's about being "better" than them.
A highly prestigious chef who caters to the wealthy and elite has any number of ways to kill if they want to, including ways that would not raise any eyebrows, such as serving fugu improperly. Fugu would even allow some plausible deniability on the chef's part, shift the blame to an underling, but name no names, say it was an accident. But Julian doesn't care about killing the guests so much as just proving he's better than them. Something like fugu poisoning would require pretending to fail, to have made a mistake, which cannot be countenanced by an elitist control freak like Julian and the prestige chefs he is based on.Slowik intended to use Tyler to target the woman he was originally dating.
Tyler has all his various insufferable traits, but nothing shown that explains why Slowick wants him in particular as part of the guest list of people he intends to kill. Slowick could have actually wanted to kill Ms. Westervelt and was merely using the convenience of Tyler being a fanatical fanboy to the end of getting her to the restaurant.Jeremy was on Slowik's grudge list.
Slowick mentions that Jeremy was a Culinary Institute of America graduate, arguably the premier American cooking school. Slowick himself worked from the bottom up, without any record showing a culinary higher education. Take that with the Eat the Rich theme and Slowik's willingness to kill Felicity for going to Brown without any student debt, and it becomes quite conceivable Slowik wanted him dead as well.Julian is a grown-up Charlie Bucket.
This is why his stories about his childhood are inconsistent. After OSHA closed the chocolate factory, he changed his name and became a burger flipper. But being unsatisfied as an older man, he remembered his old mentor Willy Wonka and invited some sinners in his very own factory. Margot is recovering from an eating disorder
Margot smokes and avoids much of the food, which may be due to a variety of factors but cigarettes are known to suppress appetites so it may have been an intentional choice. Julian is a grandson of Gustave H from The Grand Budapest Hotel, (though doesn't know it).
He has a mysterious past possibly involving eastern Europe. He's very fastidious and devoted to service. He's known to have (or at least try to) have relationships with acquaintances. His personal space is very bare, with monk-like sparsity. He has the same tendency to be Sophisticated as Hell, and he quietly despises the controlling elites, a possible reflection of what happened to his predecessor.The broken emulsion served to Lillian in the 2nd course was intentionally meant as a ‘fuck you’ to both her and the profession of food critics as a whole.
Julian doesn’t seem like the type of person who would let anything slip in his kitchen. Given that and the clear distaste he has for Lillian and the endless pursuit for perfection her profession pressures him to do, the broken emulsion could be one of the ways he’s using to express his frustration. Heck, her table could be only one that received the dish, given which table received which dish seems to be personalised somewhat, for example with the taco course. Originally, the gift bags didn't contain Doug Verrick's fingers.
As noted on the main page, we never saw his hands during his death, so his missing fingers weren't really set up. They were only mentioned in voiceover by Slowik, which is a typical method of inserting lines in post production using ADR, and the only guest that reacts is Anne, whose husband definitely had lost a finger earlier in the evening. Its ring was returned at the time, but not the finger itself - because this was when it was by to be given back, in her gift bag. Why this was changed is up for speculation: maybe it was slightly too weird (like the other things cut from the script: the shirtless dog bowl scene, the emulsion waterboarding, et cetera).