Place it right at the reveal, just as the camera catches the culprit, then follow it with a Vine Boom to underline the shock. For a slower build, start with Dun Dun Dun, let the tension settle, then let this clip ask the question.
關於此聲音
This half-second voice clip delivers the 'what you doing' line in a flat, deadpan tone, sounding like someone catching another person mid-mischief. It feels awkward, nosy and instantly funny, landing as a quick call-out rather than a question. The clipped delivery makes it easy to drop into a reaction and move on.