Why everyone agrees which blob is 'bouba' and which is 'kiki'

Show people a soft blob and a spiky star and ask which one is bouba and which is kiki. The words are made up, yet in the classic version of the test about 95% of people give the same answer: the blob is bouba.

It isn't just English or the shape of the letters. A 2022 study of 917 people speaking 25 languages found 72% matched the same way, and even 4-month-old babies seem to notice a mismatch. The likely reason is in your mouth: bouba is round lips and flowing sounds, kiki is sharp stops and a tight "ee".