Assertion: viper's fang | /r/CapableOf | fold up in the mouth
Facets:
Source sentences:
text: In Vipers, the fangs are able to fold up in the mouth when they are not in use.
text: A rhinoceros viper’s fangs fold up into its mouth, and they do not automatically appear when the mouth opens.
text: When the snakes mouth is closed the fangs fold into the back of its mouth and are covered with a membranous layer to "sheath" them.