sit open-mouthed before the screen , not screaming but yawning 
(ROOT (S (VP (VP (VB sit) (S (ADJP (JJ open) (HYPH -) (JJ mouthed))) (PP (IN before) (NP (DT the) (NN screen)))) (, ,) (S (RB not) (VP (VBG screaming)) (CC but) (NP (NN yawning))))))
(ROOT (S (VP (VP (VB ) (S (ADJP (JJ ) (HYPH ) (JJ ))) (PP (IN ) (NP (DT ) (NN )))) (, ) (S (RB ) (VP (VBG )) (CC ) (NP (NN ))))))