On reflection, the parts will hold together.
( ( On reflection ) ( , ( ( the parts ) ( ( will ( hold together ) ) . ) ) ) )
(ROOT (S (PP (IN On) (NP (NN reflection))) (, ,) (NP (DT the) (NNS parts)) (VP (MD will) (VP (VB hold) (ADVP (RB together)))) (. .)))
The part will hold together on second thought. 
( ( The part ) ( ( will ( ( hold together ) ( on ( second thought ) ) ) ) . ) )
(ROOT (S (NP (DT The) (NN part)) (VP (MD will) (VP (VB hold) (ADVP (RB together)) (PP (IN on) (NP (JJ second) (NN thought))))) (. .)))