Place this clip at the reveal frame as the first reaction, then follow a beat later with the vine boom sound for a heavier second punch, or lead into it with the dramatic dun dun dun sound to build false seriousness before the joke lands.
About this sound
This is a roughly two-second voice clip of a single speaker stretching 'oh my gahhh' into a high-pitched, rising squeal. The delivery feels theatrical and overblown rather than genuinely stunned, which makes it funny and instantly readable as mock shock. It comes from a classic Vine clip, preserved here in a cleaner take.