Out in space, above the air, stars don’t twinkle; they shine steady. But early in their work on Interstellar, Double Negative's renderer sent one perfectly thin ray from each pixel out to the stars, and a star drawn as a tiny dot is far smaller than a pixel. As it drifted, the rays hit it, missed it and hit it again, so it flickered. The usual fix is more rays per pixel, averaged, but near their black hole every ray is a long curve through bent space. So Oliver James's team didn't add rays: they gave each ray width. One soft beam per pixel, spilling into its neighbours and brightest at its heart, can't miss the star; it only catches more or less of it. The flicker fell to at most two percent, too small to notice. Real stars twinkle for another reason: moving air bends their thin thread of light, and planets shine steadier because their light arrives as a broader bundle. The same cure, twice: a wider beam.

The stars, pixels, beams and black disk here are our own drawings, not images from the film.

Which movie trick should we take apart next?

Sources: James, von Tunzelmann, Franklin and Thorne, "Gravitational lensing by spinning black holes in astrophysics, and in the movie Interstellar", Classical and Quantum Gravity, 2015 (Double Negative and Caltech); IOP Publishing press release, 13 February 2015; Crow, "The Aliasing Problem in Computer-Generated Shaded Images", Communications of the ACM, 1977; NASA Ask an Astrophysicist and Astronomy Picture of the Day on twinkling; NASA On a Mission podcast (Tracy Caldwell Dyson).
Sounds: our own, made in code (earshot, CC0).