 He grimaced at his own doubts.
( He ( ( grimaced ( at ( his ( own doubts ) ) ) ) . ) )
(ROOT (S (NP (PRP He)) (VP (VBD grimaced) (PP (IN at) (NP (PRP$ his) (JJ own) (NNS doubts)))) (. .)))
He grimaced at his doubts. 
( He ( ( grimaced ( at ( his doubts ) ) ) . ) )
(ROOT (S (NP (PRP He)) (VP (VBD grimaced) (PP (IN at) (NP (PRP$ his) (NNS doubts)))) (. .)))