Do not talk.
( ( ( Do not ) talk ) . )
(ROOT (S (VP (VB Do) (RB not) (VP (VB talk))) (. .)))
Don't say anything.
( ( ( Do n't ) ( say anything ) ) . )
(ROOT (S (VP (VB Do) (RB n't) (VP (VB say) (NP (NN anything)))) (. .)))