A scary face or object suddenly bursts into a quiet scene, along with a loud sound. The audience flinches.
Once, after you have built up enough tension. If you use it several times in one video, it gets predictable fast.
Generate two separate clips. Clip A waits quietly (static shot of an empty dark hallway, nothing happens). Clip B is a short clip where a face suddenly appears close to the camera. In the edit, hold A for a good while, then attach B with a hard cut. Turn off the generated audio and line up a loud sound effect on B's first frame with adelay. Keep B short, 0.5 to 1 second, so the AI glitches that warp faces are less noticeable.
Two-shot sequence: Shot 1, a girl in an empty night library slowly walks between tall bookshelves, a flashlight beam sweeping, very quiet, no music, 4 seconds; hard cut to Shot 2, a pale figure bursts into the frame at the end of the aisle, face close to the camera, with a sudden loud crash sound, 1 second.
Cat People (1942) — The film builds quiet tension and then breaks it with a loud sound, a cut and fast movement, creating the jump scare in the editing. This device is also called the "Lewton bus" (Wikipedia — Jump scare) · Carrie (1976) — The ending, where an arm shoots out of the soil, inspired the final jump scare in Friday the 13th (1980) (Wikipedia — Jump scare)
Not verified