Bong has some ideas in “Parasite,” but the movie’s greatness isn’t a matter of his apparent ethics or ethos — he’s on the side of decency — but of how he delivers truths, often perversely and without an iota of self-serving cant. (He likes to get under your skin, not wag his finger.) He accents the rude comedy of the Kims’ struggle with slyness and precision timing, encouraging your laughter. When the son and daughter can’t locate a Wi-Fi signal — the family has been tapping a neighbor’s — they find one near the toilet (an apt tribute to the internet). And when a cloud of fumigation billows in from outside, an excited Ki-taek insists on keeping the windows open to take advantage of the free insecticide. They choke, you laugh. You also squirm.

The lightly comic tone continues after the Kims begin working for the Parks, despite ripples of unease that develop into riptides. Some of this disquiet is expressed in the dialogue, including through the Kims’ performative subservience, with its studied courtesies and strategic hedging. (Bong shares script credit with Han Jin Won.) The poor family quickly learns what the rich family wants to hear. For their part, Mr. and Mrs. Park (Lee Sun Kyun and Cho Yeo Jeong) speak the language of brutal respectability each time they ask for something (a meal, say) or deploy a metaphor, as when he gripes about people who “cross the line” and smell like “old radishes.”

The turning point comes midway through when the Parks leave on a camping trip, packing up their Range Rover, outdoor projector included. In their absence, the Kims bring out the booze, kick back and take over the house, a break that’s cut short when the old housekeeper returns, bringing a surprise with her. The slapstick becomes more violent, the stakes more naked, the laughs more terrifying and cruel. By that point, you are as comfortably settled in as the Kims; the house is so very pleasant, after all. But the cost of that comfort and those pretty rooms — and the eager acquiescence to the unfairness and meanness they signify — comes at a terrible price.

Parasite

Rated R for class exploitation and bloody violence. In Korean, with subtitles. Running time: 2 hours and 12 minutes.