Quoting Jorge Llambías <jjllambias@gmail.com>:
One distinction is that skapi is a kind of material ("from x2")
while pilka is a body-part ("of x2"). So pilka only becomes skapi
once it has been removed from the animal it belonged to.
Somewhat analogous to the distinction between "meat" and
"flesh" in English.
So human skin is "rempi'a" then? mu'o mi'e. bret.