#protective_fold  a flap of tissue that protects what it covers
  supertype:  flap.animal_tissue  a movable piece of tissue partly connected to the body
  subtype:  eyelid__lid  either of two folds of skin that can be moved to cover or open the eye; "his lids would stay open no longer"
  subtype:  nictitating_membrane__nictitatingmembrane__thirdeyelid  a protective fold of skin in the eyes of reptiles and birds and some mammals
     subtype:  haw  the nictitating membrane of a horse

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