( She ( ( ( rocked ( her groin ) ) ( against ( his cock ) ) ) . ) )
(ROOT (S (NP (PRP She)) (VP (VBD rocked) (NP (PRP$ her) (NN groin)) (PP (IN against) (NP (PRP$ his) (NN cock)))) (. .)))
She rocked her groin against his cock.
(ROOT (S (NP (NP (DT A) (NN wall)) (PP (IN of) (NP (NP (NNS rocks)) (CC or) (NP (JJ concrete) (DT a))))) (VP (VBD called) (NP (DT a) (NN groin))) (. .)))