, though many of the actors throw off a spark or two when they first appear , they ca n't generate enough heat in this cold vacuum of a comedy to start a reaction . 
(ROOT (S (, ,) (SBAR (IN though) (S (NP (NP (JJ many)) (PP (IN of) (NP (DT the) (NNS actors)))) (VP (VBP throw) (PRT (RP off)) (NP (DT a) (NN spark) (QP (CC or) (CD two))) (SBAR (WHADVP (WRB when)) (S (NP (PRP they)) (ADVP (RB first)) (VP (VBP appear))))))) (, ,) (NP (PRP they)) (VP (MD ca) (RB n't) (VP (VB generate) (NP (NP (JJ enough) (NN heat))) (PP (IN in) (NP (NP (DT this) (JJ cold) (NN vacuum)) (PP (IN of) (NP (DT a) (NN comedy))))) (S (VP (TO to) (VP (VB start) (NP (DT a) (NN reaction))))))) (. .)))
(ROOT (S (, ) (SBAR (IN ) (S (NP (NP (JJ )) (PP (IN ) (NP (DT ) (NNS )))) (VP (VBP ) (PRT (RP )) (NP (DT ) (NN ) (QP (CC ) (CD ))) (SBAR (WHADVP (WRB )) (S (NP (PRP )) (ADVP (RB )) (VP (VBP ))))))) (, ) (NP (PRP )) (VP (MD ) (RB ) (VP (VB ) (NP (NP (JJ ) (NN ))) (PP (IN ) (NP (NP (DT ) (JJ ) (NN )) (PP (IN ) (NP (DT ) (NN ))))) (S (VP (TO ) (VP (VB ) (NP (DT ) (NN ))))))) (. )))