They're both excited about it ...
( They ( ( ( 're both ) ( excited ( about it ) ) ) ... ) )
(ROOT (S (NP (PRP They)) (VP (VBP 're) (DT both) (ADJP (JJ excited) (PP (IN about) (NP (PRP it))))) (: ...)))
They're excited about the zoo. 
( They ( ( 're ( excited ( about ( the zoo ) ) ) ) . ) )
(ROOT (S (NP (PRP They)) (VP (VBP 're) (VP (VBN excited) (PP (IN about) (NP (DT the) (NN zoo))))) (. .)))