Da-song realizes something's weird about the Kim family, although (understandably for a little boy) he isn't truly able to connect the dots. His way of conveying this suspiciousness to his family, however, is through pointing out that the Kims have the same odor. The Park parents dismiss this... because to them, especially Mr. Park, poor people just tend to smell bad. It actually foreshadows their classism rather than simple good-natured trust for the Kims, which in Mr. Park's case is so present that it's his literalFatal Flaw.
During the birthday massacre, Ki-taek is wearing the same exact grey shirt that Ki-woo was wearing in the very first scene, symbolizing they are back where they started.
The rock floated in the flood scene. It's a fake rock, an empty promise of social mobility in a capitalistic society.
Both of the most tense scenes in the movie are introduced by songs in Italian, 'In Ginocchio Da Te' and 'Mio Caro Bene', both of which hint at how they will end; In Ginocchio Da Te is a pop love song, which hints that the Kims will be able to escape, and 'In Ginocchio' (On My Knees) is also an Italian expression that means 'I'm completely broke and defeated', alluding to the flood that destroys their home and leaves them homeless. 'Mio Caro Bene', instead, is an aria from a drama, which hints it won't end well, and the opera it is from ends with a stabbing.
Min says that Ki-woo has "taken the college exams 4 times". Considering he can't afford college, it's implied the protagonist took the college exams in rich people's place to get them into school, and that's how his friend was so sure he could teach the Park daughter.
More likely that he took it 4 times in hopes of getting better grades and be accepted to a more prestigious university, which is often the case in Korea. This implies that the family wasn't always as poor as they are in the film, since re-taking exams costs more.
Ki-woo states that Ki-jeong is the only one in their family who really suits the opulent lifestyle of the rich. He means it as a compliment; his charming, clever sister indulges in the Park mansion's amenities as though she's had access to such luxury all her life. However, Ki-jeong dies, and is also the sole Kim to die in the film. This reflects a realization that Ki-woo well has by the time their greed has caught up to them: that the status of the obscenely wealthy, like the Parks, is not that admirable. Rich people like the Park family step on the backs of the lower classes to exist the way they do, which is why Ki-jeong — the one most suited to a life like that — is the Kim who dies. Ki-woo, his mother, and his father belong to the less lavish world of the working classes no matter how much they attempt to social-climb, but by the end of the film they're the ones still alive to build better futures for themselves. It's also notable for the fact that the least sympathetic, and the most elitist, of the Parks is also the only member of his family who dies (Dong-ik).
Additionally, the reason Ki-jeong is so "at home" in the upper-class environment is that she is the most ruthless. She chastises her family for starting to feel guilt for knocking the former employees down because she already knows and accepts that oppressing others is what it means to stay at the top.
But then it switches. Ki-jeong is the only one who tries to take the food down to the basement at the end of the film, and shows concern for the Parks — which shows that while she can pretend to be ruthless, she isn't at her core. She can try to belong, but she never will.
Overlapping with Fridge Horror: early in the film, the Kims are seen folding pizza boxes while the fumigator sprays thick clouds of pesticide into their home. People are going to be eating food out of those boxes. This scene perfectly reinforces the movie's overall critique of capitalism by demonstrating how the ruthless cost-cutting by the pizza company and their subcontractors creates a dangerous situation for unsuspecting consumers.
Da-song has a habit of drawing wide-eyed faces. While the drawings are assumed by Mrs. Park to be self-portraits, they bear more of a resemblance to a certain wide-eyed face Da-song saw once before: that of Geun-se.
The poor family is always descending into their architecture. Meanwhile the rich family is always moving up the stairs. Perfect symbolism.
The bunker, which is the area deepest underground in the film, is also where the people lowest on the social ladder live, the dispossessed, indebted, and criminals. The rich Parks have no idea of its existence because the architect hid it out of embarrassment, just as they have little awareness of the troubles of the lower class whose backs they stand on.
The rock being used as the "weapon" which falls down the stairs is an allegory for how hope is the biggest parasite. While it gives people the ability to move forward, it is elusive and feeds on their hard work. Their hope exploits them while never truly giving them a future, much like in the way the rock is seen as a symbol of good luck but is just a false veneer of possibilities. It's not real, which is why the mother said "You could've given us real money" when they were given the rock.
The rock also floats in the flood, indicating that it's hollow and fake, just like the hope of upward mobility that the family put on it. This also explains how Ki-woo survives being hit over the head with it.
Alternatively the rock scene could be interpreted as Ki-woo's imagination since a rock doesn't naturally float. Him imagining the impossible shows him believing in their social ascension which is just as improbable. Then the light flickers and goes dark, signifying his urge to murder the people detrimental to his plan using that very rock, symbolizing his hope descending into bloodthirsty avarice. During the epilogue him returning the rock to the creek shows that he made his peace with the fact that his dreams are just that, dreams. The rock itself climbed the social ladder by becoming an artistic piece from a mere rock, but in the end it returned to nature where it belonged to, not unlike Ki-woo.
Tropical fruit that has to be imported can be quite pricey to afford on a daily basis in Japan/Korea, yet the Parks eat it so casually all the time.
Although the Parks are frivolous and condescending, they aren't mean. It's showing the rich aren't just one-sided "evil". Rather, their naivety and entitlement is what made them unbearable. They can't help they were born rich, and raised with that mentality. They aren't bad people. They, like everything else, are almost unknowingly playing into a system they've been adjusted to their whole lives. It only takes the truly self-aware and destitute to see the truth of that manipulative social situation.
Ki-woo splashing water on the homeless man peeing outside is yet another display of the poor fighting each other and never wanting to be in that "lowest position". The slow-motion water hosing while the man pees suggests that the human desire to organize each other and look down upon those lower than us is one of the biggest reasons that the poor can never restore social balance. If we constantly are looking at those lower than us, it's hard to look at those above us.
When Ki-woo lands his job as a tutor at the Parks' house, the first thing the family does is celebrate by drinking the "Flight" beer, which is the cheapest beer in Korea. When Ki-jeong also gets hired by the Parks, all of the members of the family, with the exception of Chung-sook, move on to drinking "Sapporo," which is a Japanese brand and is one of the best quality beers that you can find in regular Korean supermarkets (about twice as expensive as "Flight"). Chung-sook continues to drink "Flight," which may represent a mother's love and constant willingness to make sacrifice for the sake of her children. Unlike Geun-se and Ki-taek who commit murder out of hate toward the members of a different class, Chung-Sook commits murder as a revenge for her daughter's death (which is also the reason why she doesn't get sentenced to jail but remains living freely with her son in their old house). This may describe many Korean mothers (or 'ahjummahs') who disregard etiquette or trends and prefer practicality over all.
There is a scene where Moon-gwang wakes up Yeon-kyo Park; in it, a line created from two panes of glass meeting separates the two of them. The house is full of lines. Stairway, hallway… the rich and poor seems to always stay on opposite sides of the line.
The Park family is even further risen from being at the top of the hill by having their entrance to their main area of living involve walking up a case of stairs while, in contrast, the Kim's family, as already mentioned, goes even lower than the bottom as the hill as they live in a semi-basement. Higher than high and lower than low.
Ki-jeong/Jessica's death can be interpreted this way: Her job is to help alleviate the son's trauma through art therapy, the trauma brought on by the "ghost" in the basement. Throughout the film, she is lying and deceiving them; she is the only one working for the family that isn't actually helping the family, and is only leeching off them. She has not gotten rid of the ghost. Her punishment is the ghost stabbing her, and Da-song's need for medical attention, which she was supposed to cure, seals her fate.
The Parks are emotional parasites as well. Da-hye is desperate for someone to understand her, hence her feelings for her tutor. The son is in need of a true mother figure, Yeon-kyo is in need of a therapist, and Dong-ik is in need of a friend. While they're rich, they're easily gullible and roped into the Kim's antics precisely because their rich life seems so fake — as shown by the Park mother's implied drug addiction and constant state of sleepiness. While they do have money, they aren't shown to necessarily be "happy". Customers who overstep boundaries and act like employees are friends or confidants is very common in the service industry, and possibly stems from the false veneer of friendship which is displayed in elite culture.
Bong Joon-ho says in an interview that Yeon-kyo "dreams of a world that is bright and very fresh. But she's actually trapped in this glass box that she's made for herself. She's obsessed with her young son, but she never hugs him. There's no physical intimacy between them, regardless of how much she adores him." The scene in which Ki-taek offers a friendly hand to her, but she recoils because she doesn't know if Ki-taek has washed his hand, makes even more sense with this in mind. She's lonely and desperate for intimacy and companionship, but has stuck herself in a glass box, like a flower too delicate to be left outside in the real world, where things can be a little dirty or messy. The price is a life that's sheltered and shiny, but utterly devoid of real warmth. Also notable in this context is how, when engaging in sexual activity with her husband, one of the few moments we actually see her indulging in physical intimacy with someone, they're either roleplaying or she's asking for drugs — either way, she isn't entirely herself.
The note about there being "no physical intimacy" between Yeon-kyo and Da-song also explains why Ki-jeong is able to keep him calm and why he becomes so fond of her. Each time we see one of her "lessons", Ki-jeong has Da-song cradled in her lap and is obviously paying him her undivided attention. He's starved for this sort of physical contact from a maternal figure and doesn't want to lose it.
Chung-sook kicking Moon-gwang down the stairs isn't just a gag or plot point, it's a metaphor for what her family has done. Trying to climb the stairs to a better life, they've knocked down other people who wanted the same thing. They pay little mind to the damage done as a result since it's out of sight, such as Moon-gwang's fatal head wound and the uncertain fate of the driver Yoon.
Da-song doing nothing when seeing the lights. Geun-se is communicating through lights and Da-song thought he saw a ghost. Flickering lights are often associated with spirits and spectres. The "help me" messages may have just scared the kid further.
Ki-jeong pulls off a masterful Batman Gambit by leaving her panties in Mr. Park's car, which leads him to fire his driver Yoon and replace him with Ki-taek. When Mr. and Mrs. Park discuss the matter, they conclude that Yoon had sex in the backseat with a woman who was so messed-up on drugs she forgot to put her panties back on. Then later in the film, while they lay on their couch to keep an eye on Da-song outside, the Parks re-enact this scenario as sexual roleplaying. But, of course, it never actually happened to Yoon. Instead, they were projecting their own kinky fantasies onto him all along.
Ki-jeong is talented at art and graphic design, but it never got her anywhere until she started lying about her connections and background. The kid she tutors, Da-song, is praised by his mother as a "genius" in art even though he's really just a normal child who likes to draw and paint, like many other children. Da-song is set for a life of being praised and succeeding even if he's just average or mediocre due to his background and familial connections, whereas poor people like Ki-jeong can be tremendously talented but not considered good enough without connections.
Da-song is obsessed with Native American culture, but only in a superficial Braids, Beads and Buckskins manner. He plays with toy arrows and his father plays with him by acting as a 'savage Indian' trope. In recent years, the commodification of First Nations culture has become controversial in the West, as First Nations people (who are often subject to racism and poverty) see their identity being reduced to something to be bought and sold. In this way, Da-song is acting just like the rest of his family; he is picking up and playing with another peoples' culture in the same way that his parents hire and order around their servants; and he will likely lose interest and forget about this passing obsession in the same way his parents will casually throw aside the people who work for them.
Why did Geun-Se have such a terrifying expression on his face the night he traumatized Da-Song? Because he probably didn't in reality. We're seeing that scene through Da-Song's eyes, and seeing a strange man come out of your basement would be utterly terrifying, especially in the dark with Geun-Se's odd facial features. He likely never intended to scare the poor kid in the first place.
At the beginning of the film, Min-hyuk goes off to study abroad. Presumably, at some point, he will return and discover that his recommendation of Ki-woo unwittingly led to several deaths.
Ki-taek's lifestyle in the bunker is all but certainly doomed to failure without somebody aiding him on the outside. Given he already killed somebody while still sane, there's a good chance he might simply snap and kill everyone in the house when he's discovered to protect himself.
Da-song was already traumatized enough from his previous birthday experience and now he had to witness the death of the woman who helped him recover from it. Not to mention he's lost his father, who he has been shown to care about a lot. Unless Mrs. Park is able to invest in a really good therapist (and possibly a psychiatrist), Da-song is going to have some serious mental issues growing up.
Min isn't as much of a good guy as he seems. He gives Ki-woo the prosperity stone, which is a metaphor for the promise of wealth, but much more than that it is the symbol for hope. Ki-taek knew all along that hope is fulfilled for the rich, but it only brings discontentment for the poor, so it is better to not care about anything. Min isn't so much intentionally giving Ki-woo the rock to curse him, though he does; he is giving it to him because he does not know better. He is blind to see the problems of the lower class, as all the upper-class characters are.
Also, Min intentionally goes to Ki-woo because he looks down on him, thinking that while his rich university friends might be able to steal his girlfriend, Ki-woo is too poor and Da-Hye would never go for him because Ki-woo wouldn't fit in with her and her family. Ki-woo seems to realize this and rebel against the very idea, which is why he starts to pursue Da-Hye, even though it never really seemed like he liked her for her as much as for the idea of her as a trophy and rebellion against Min's poor view of him.
It doesn't end with the dream... it ends with that dream shattered; it ends with the man dreaming locked in his semi-basement looking towards us, because we know that that dream is simply not possible. Even the director himself stated he explicitly wanted the ending to kill any hope.
In a scary Rule of Symbolism way, Ki-Jeong's death and the downfall of the Kim family was foreshadowed. When the family is celebrating their plan against the Parks becoming a success, and Ki-woo and Ki-teak start to feel guilt and hope the people they deceived like The Driver are able to get back on their feet, a drunken Ki-Jeong lashes out at them and claiming the only people they should care about is themselves and forget everyone else. A violent lightning strike happens afterwards as it starts to rain. Ki-woo and Ki-teak joke about it, but soon afterwards, everything starts going to hell. Their celebration was literally the calm before the storm.
that Yeon-kyo "dreams of a world that is bright and very fresh. But she's actually trapped in this glass box that she's made for herself. She's obsessed with her young son, but she never hugs him. There's no physical intimacy between them, regardless of how much she adores him." The scene in which Ki-taek offers a friendly hand to her, but she recoils because she doesn't know if Ki-taek has washed his hand, makes even more sense with this in mind. She's lonely and desperate for intimacy and companionship, but has stuck herself in a glass box, like a flower too delicate to be left outside in the real world, where things can be a little dirty or messy. The price is a life that's sheltered and shiny, but utterly devoid of real warmth. Also notable in this context is how, when engaging in sexual activity with her husband, one of the few moments we actually see her indulging in physical intimacy with someone, they're either roleplaying or she's asking for drugs — either way, she isn't entirely herself.