Place it near the start of a reaction video so the audience test comes before any reveal, then follow the answers with a Bell Ding for a yes and the Dramatic Dun Dun Dun for a no, and finish with an Anime Wow when a younger viewer hears it instantly.
About this sound
This is a short, very high-pitched electronic tone lasting about four and a half seconds, thin and sharp enough to feel like a faint whine at the edge of hearing. It creates playful suspense and disbelief, as listeners compare who catches it and who hears nothing at all. It spread through Spanish-language short-form videos captioned Solo lo escuchan los jóvenes, meaning only young people can hear it.