[markburns]

That seems to me like it just shifts the problem one level. Why are K's and Kikis spiky and why are B's and Boubas round. Why is it universal too across people with different writing systems and languages.

[chickenimprint]

I can think of so many counterexamples on the spot: Latin, Arabic, Hebrew, Japanese syllabaries. It's really only the Greek Kappa that is spiky.