Assertion: bald eagle's beak | /r/MadeOf | keratin
Facets:
Source sentences:
text: The beak, talons, and feathers are made of keratin.
text: The beak, talons, and feathers are made of keratin.
text: The beak, talons, and feathers are made of keratin, which is also the key structural component of human hair and nails.