So what is the explanation of the phrase cold enough to freeze the balls off a brass monkey ?  Well, the obvious one, I believe.
( So ( ( what ( is ( ( the explanation ) ( of ( ( the phrase ) ( ( cold enough ) ( to ( ( freeze ( the balls ) ) ( off ( ( ( a ( brass ( monkey ( ? Well ) ) ) ) , ) ( the ( obvious one ) ) ) ) ) ) ) ) ) ) ) ) ( , ( I ( believe . ) ) ) ) )
(ROOT (S (IN So) (SBAR (WHNP (WP what)) (S (VP (VBZ is) (NP (NP (DT the) (NN explanation)) (PP (IN of) (NP (NP (DT the) (NN phrase)) (ADJP (JJ cold) (RB enough) (S (VP (TO to) (VP (VB freeze) (NP (DT the) (NNS balls)) (PP (IN off) (NP (NP (DT a) (NNP brass) (NNP monkey) (. ?) (NNP Well)) (, ,) (NP (DT the) (JJ obvious) (NN one)))))))))))))) (, ,) (NP (PRP I)) (VP (VBP believe)) (. .)))
Some expressions have a very obvious meaning.
( ( Some expressions ) ( ( have ( a ( ( very obvious ) meaning ) ) ) . ) )
(ROOT (S (NP (DT Some) (NNS expressions)) (VP (VBP have) (NP (DT a) (ADJP (RB very) (JJ obvious)) (NN meaning))) (. .)))