( ( ( The muscles ) ( in ( their abdomen ) ) ) ( ( ( ( are ( very strong ) ) and ) ( help ( keep ( ( the animals ) ( ( ( curled up ) even ) ( when ( predators ( are ( trying ( to ( pry ( them open ) ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (NNS muscles)) (PP (IN in) (NP (PRP$ their) (NN abdomen)))) (VP (VP (VBP are) (ADJP (RB very) (JJ strong))) (CC and) (VP (VBP help) (VP (VB keep) (SBAR (S (NP (DT the) (NNS animals)) (VP (VBD curled) (PRT (RP up)) (ADVP (RB even)) (SBAR (WHADVP (WRB when)) (S (NP (NNS predators)) (VP (VBP are) (VP (VBG trying) (S (VP (TO to) (VP (VB pry) (S (NP (PRP them)) (ADJP (JJ open)))))))))))))))) (. .)))
The muscles in their abdomen are very strong and help keep   the animals curled up even when predators are trying to pry them open.
(ROOT (S (NP (JJ Strong) (NN odor)) (VP (VBZ helps) (S (NP (DT some) (NNS animals)) (VP (VB defend) (NP (PRP themselves)) (PP (IN against) (NP (NNS predators)))))) (. .)))
Strong odor helps some animals defend themselves against predators.