And for some reason, "kakka" is de facto word for excrement in Finnish, which is from the Uralic family.
It is very weird seeing it here, because it's like THE word.
kakka is more like "poop" and the rougher word "shit" has a different word (paska[Learning about the homophone-y Pascal is always a knee-slapper])
I think that it's a parallel development. It's unlikely to be a borrowing from some PIE descendant because
*NOTE: before someone mentions German "kacken", it's likely a borrowing from Latin "cacō" I shit. Now that's some borrowed shit!