Assertion: hedgehog's spine | /r/HasProperty | made of keratin
Facets:
Source sentences:
text: They are covered with a coat of very sharp spines, which are hollow and made of keratin (like your fingernails).
text: Of course, since he's known as a pincushion on legs, you can't overlook the hedgehog's quills, the dense spines made of keratin covering his back.
text: Hedgehogs have long spines, or quills, made of keratin.