Assertion: porcupine's quill | /r/HasProperty | exposed to air
Facets:
Source sentences:
text: These soft quills harden with days while being exposed to air.
text: The porcupine baby, called a porcupette, comes into the world with eyes open and a full coat of spines, but the quills are soft and rubbery, and only harden when exposed to the air.