Put it at the end of the suspicious setup, right after the claim is shown, then follow it with Eww Brother Eww for a second, stronger dismissal. For a slower build, open with Sudden Suspense before the reveal so the judgement hits as the payoff.
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This is a short Portuguese spoken reaction, lasting about two and a half seconds, in which a voice delivers the line 'Isso me cheira a merda' with blunt disgust. It lands as a suspicious, nose-wrinkling judgement, funny because it treats a bad idea or shady claim like something rotten. The delivery is direct and dismissive, made for calling out something that simply does not feel right.