Assertion: toenail | /r/MadeOf | tough protective protein
Facets:
Source sentences:
text: Fingernails and toenails are made of a tough protective protein called alpha-keratin which is found in the hooves, hair, claws and horns of vertebrates.
text: Fingernails and toenails are made of a tough protective protein called keratin.
text: Fingernails and toenails are made of a tough protective protein called alpha-keratin which is a polymer and found in the hooves, hair, claws and horns of vertebrates.