Assertion: emu's skin | /r/HasProperty | tough
Facets:
value: to peneterate like mammals
type: PURPOSE
Source sentences:
text: While most birds have thin skin and hollow bones to make them lighter for flying, the kiwi’s skin is a bit thicker and tough, and its bones are heavy and filled with marrow.
text: The skin of these birds is tough and hard to peneterate just like mammals.