Assertion: echidna's spine | /r/HasProperty | stiff
Facets:
Source sentences:
text: The spines are stiff and made of bone-like calcified material.
text: The spines are generally straw-coloured with black tips, and are both strong and sharp.
text: They have fur (their spines are actually stiff hairs), they are warm-blooded, and they produce milk for their young.