Okja's design was based on the face of a manatee and the body of a hippopotamus. The hippopotamus-like design was specifically chosen as a reference to the infamous 1910 "Hippo Bill," which proposed the idea of America importing, breeding and farming hippopotamuses for meat.
There is a deliberate mistranslation of the English subtitles when K, played by Steven Yeun, is about to jump out of the truck at the beginning. According to the subtitles, his parting words to Mija are "Mija! Try learning English. It opens new doors!" What he actually says in Korean is "Mija! Also, my name is Koo Soon-bum." It's a flagrant mistranslation - but one that would only be apparent to those who can speak both languages. Moreover, the mistranslation is a clever subversion of the supremacy of English. The subtitle is a command to learn English - something every Korean student has heard throughout their life. But to actually understand what K is saying, you would have to know Korean. There's an added layer of comedy to the name itself, which has the whiff of the old country about it: "Koo Soon-bum" is sort of like a white man saying his name is "Buford Attaway." As Yeun said in an interview, "When he says 'Koo Soon-bum,' it's funny to you if you're Korean, because that's a dumb name. There's no way to translate that. That's like, the comedy drop-off, the chasm between countries."
When the movie premiered at the Cannes Film Festival, the audience began to boo when the Netflix's title card was shown in the opening credits, they then followed up by showing the first 10 minutes of the film in the wrong ratio causing more booing. The film was played again from the beginning with even louder boos when the Netflix's title card was shown for the second time.
Bong Joon Ho and his producer Dooho Choi visited a real slaughterhouse in Colorado to prepare for the scene in the film. The visit temporarily converted the two into vegans.
During the New York parade scene, Tilda Swinton wears a traditional Korean dress called "Han Bok". Korean Han Bok are usually very colorful with red, blue and other bright colors, but Swinton's matches her limited two-color palette.