They should have him be just a disembodied voice.
( They ( ( should ( have ( him ( be ( just ( a ( disembodied voice ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP They)) (VP (MD should) (VP (VB have) (S (NP (PRP him)) (VP (VB be) (NP (RB just) (DT a) (JJ disembodied) (NN voice)))))) (. .)))
The entity should not be seen, only heard.
( ( The entity ) ( ( ( ( ( ( should not ) ( be seen ) ) , ) only ) heard ) . ) )
(ROOT (S (NP (DT The) (NN entity)) (VP (VP (MD should) (RB not) (VP (VB be) (VP (VBN seen)))) (, ,) (ADVP (RB only)) (VP (VBD heard))) (. .)))