banged their brains into the ground 
(ROOT (S (VP (VBD banged) (NP (PRP$ their) (NNS brains)) (PP (IN into) (NP (DT the) (NN ground))))))
(ROOT (S (VP (VBD ) (NP (PRP$ ) (NNS )) (PP (IN ) (NP (DT ) (NN ))))))