Here is the Wikipedia article about the phenomenon of the bouba–kiki effect if you prefer text form or want to know more about it: https://en.wikipedia.org/wiki/Bouba%2Fkiki_effect

One of my favourite nerdy jokes is that the Fourier transform is a bouba-kiki transform.

This phenomenon of "sound symbolism" has received a lot of research attention in the last 10 years or so. For a long time it was considered a curiosity at best, and a total red herring at worst, but a lot of evidence is accumulating that sound symbolic effects are very real and may have profound implications for our understanding of sensorimotor cognition.

The shapes just look like the letters. K’s have sharp corners, B’s are round.