that gradually sneaks up on the audience 
(ROOT (S (NP (DT that)) (ADVP (RB gradually)) (VP (VBZ sneaks) (PRT (RP up)) (PP (IN on) (NP (DT the) (NN audience))))))
(ROOT (S (NP (DT )) (ADVP (RB )) (VP (VBZ ) (PRT (RP )) (PP (IN ) (NP (DT ) (NN ))))))