Dae-su eats a live octopus in a sushi restaurant. According to IMDb, 4 live octopodes were eaten by the actor to accomplish the scene in the sushi bar.
There is never any actual assault on camera but a lot of close calls. Most of the movie revolves around sex, and desire that feels nonconsensual. Particularly involving womens bodies. Also a lot of coercion. This movie triggered me more than ones with quick assault scenes that I can just mute for a couple of minutes. If this is your trigger I would not recommend watching, or really taking care while watching.
There are several mentions of suicide. A side character kills themselves by jumping off a tall building with their dog in their arms. Someone’s sister dies by suicide. Also a character dies by suicide with gunshot to their head.