Place this clip right after the reveal in your edit, then follow it with the fahhh meme sound for a second person joining the reaction. For a bigger pile-on, end the sequence with the anime wow sound button once everyone has reacted.
關於此聲音
The clip is a single stretched-out 'Ihhh' exclamation lasting just over five seconds, held far longer than a normal reaction. It sounds like someone recoiling from something gross or unsettling. That drawn-out discomfort is what makes it funny, giving listeners an instant feeling of disgust mixed with nervous, awkward laughter.