wallowing in its characters ' frustrations 
(ROOT (S (VP (VBG wallowing) (PP (IN in) (NP (NP (PRP$ its) (NNS characters) (POS ')) (NNS frustrations))))))
(ROOT (S (VP (VBG ) (PP (IN ) (NP (NP (PRP$ ) (NNS ) (POS )) (NNS ))))))