What Do You Hear? is a TikTok video trend and social game in which audio is played in the background while various words are displayed on-screen. The idea is that the audio is muddled in a way that when you hear it, your brain will change what it hears based on what words you are reading on the screen, even though the audio itself never changes.
On October 20th, 2019, TikToker Monkey Seb [1] created the first original sound on TikTok that was used in videos doing this trend. His video [2] received 1.5 million likes and spawned over 11,600 videos in two years (shown below).
This trend of audio mishearing spread around as other creators using their own original sounds added to it.