( They ( ( are ( herbivores ( which ( means ( they ( only ( eat ( plant life ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP They)) (VP (VBP are) (NP (NP (NNS herbivores)) (SBAR (WHNP (WDT which)) (S (VP (VBZ means) (SBAR (S (NP (PRP they)) (ADVP (RB only)) (VP (VBP eat) (NP (NN plant) (NN life)))))))))) (. .)))
They are herbivores which means they only eat plant life.
(ROOT (S (NP (NNS Herbivores)) (VP (VBP are) (NP (NP (NNS heterotrophs)) (SBAR (WHNP (WDT that)) (S (VP (VBP eat) (NP (UCP (ADJP (JJ only)) (CC or) (ADVP (RB mainly))) (NNS plants))))))) (. .)))