serves as a rather thin moral to such a knowing fable 
(ROOT (S (VP (VBZ serves) (PP (IN as) (NP (NP (DT a) (ADJP (RB rather) (JJ thin)) (NN moral)) (PP (IN to) (NP (PDT such) (DT a) (VBG knowing) (NN fable))))))))
(ROOT (S (VP (VBZ ) (PP (IN ) (NP (NP (DT ) (ADJP (RB ) (JJ )) (NN )) (PP (IN ) (NP (PDT ) (DT ) (VBG ) (NN ))))))))