Assertion: hoatzin's muscle | /r/ObjectUse | used for flight
Facets:
Source sentences:
text: However evolution operated on part of their digestive anatomy called the crop a feture common to birds to make it function much like a cow's rumen and as a result the crop is so large that it displaces muscles that otherwise would have been used for flight ..
text: As a result, the crop is so large that it displaces muscles that otherwise would have been used for flight.