that will keep them guessing 
(ROOT (SBAR (WHNP (DT that)) (S (VP (MD will) (VP (VB keep) (NP (PRP them)) (S (VP (VBG guessing))))))))
(ROOT (SBAR (WHNP (DT )) (S (VP (MD ) (VP (VB ) (NP (PRP )) (S (VP (VBG ))))))))