Place it as the reaction beat right after a reveal or a question, then follow it with a contrasting payoff such as the sad violin sound button for a fake letdown, or kids cheering for genuine approval.
このサウンドについて
A very short vocal clip of a drawn-out 'mmmm' hum, lasting under a second, with no words, just a single satisfied-sounding tone held briefly. It gives a light, amused feeling of approval or tasty enjoyment, like someone quietly agreeing, savouring something good, or pretending to think hard before answering.