hitting your head on the theater seat 
(ROOT (S (VP (VBG hitting) (NP (PRP$ your) (NN head)) (PP (IN on) (NP (DT the) (NN theater) (NN seat))))))
(ROOT (S (VP (VBG ) (NP (PRP$ ) (NN )) (PP (IN ) (NP (DT ) (NN ) (NN ))))))