Place it immediately after the reveal in a short edit, then let Awkward Crickets follow to hold the pause a little longer. If the moment needs a bigger reaction instead, swap in Yoooooooooooo after the same beat and keep the rest of the edit unchanged.
Over dit geluid
This clip is a very short human vocalisation, a drawn-out 'ahh' that lasts less than a third of a second. The single stretched vowel lands as a quick burst of mock surprise or sudden realisation, funny because it is over almost as soon as it begins. It works as a tiny reaction, the kind of sound that punctuates a moment without explaining it.