Trolls cannot have belly buttons
The only reason creatures have belly buttons is because of the umbilical cord they were attached to while inside their mother’s womb. If the Homestuck trolls were hatched as grubs then evolved, there’s no way they can have belly buttons!
I only say this because I constantly see pictures of trolls with belly buttons. And I don’t know why but it bothers me anatomically
THUS I rest my case
…and because they are not mammals, they also can’t have nipples