I. The central question

Q: What's the connection between Su Tungpo's protest poetry and his arrest and trial?

A: Su Tungpo's protest poetry was not the reason he was caught, but it had important influence on his trial. Su Tungpo wrote something to criticized the politic wich made Wang Anshih and his followings uncomfortable. They just made up his charges then arrested him. This thing called The Case of Poetry at the Black Terrace. In one word, Su Tungpo's integrity and straightforward incur this frustration. However, it's influence was more than that. When Su Tungpo started his politic life in Huangchow, even he didn't gave up writing poems but the numbers were descend. He tried to use more time and energy to writing tse, another style of traditional peotry.

II. The sentense

1. Su Tungpo, to use the poet's own expression, had gone on "spitting out flies found in one's food,"  and had so far escaped scot-free. But the hundredth time he "spat", he was caught.

scot-free    to avoid being punished although you deserve to be.

"But the hundredth time he "spat", he was caught." 化用苏东坡所说原句，这一句中十分风趣。

2. Ancient scholars, in the absence of protection of civil rights, had developed an extreme subtlety in phrasing, saying more than was apparent, and scholar readers had developed the habit of hunting with delight for what was said between the lines.

这一句中将文人的婉转隐语归结为the absence of protection of civil rights未免不太得当。首先，用隐语本身是古代文人的传统，如怨刺、雅怨，合乎诗骚之旨。其次，古代文人真的没有人身权益吗？当然未必，就宋代一朝，虽有因言获罪的情况，但更多的是君臣遇合，共治国政，用现代人的眼光去审视古代社会，未免有失偏颇。

3. Incorrigible as he was, that very day he wrote two poems again wherein he said that "facing the wine cup" he "felt like coming out of a dream," and trying his poetic pen, he "found it was already inspired."

incorrigible  someone who is incorrigible is bad in a way that cannot be changed or improved – often used humorously

这个词在结尾出现了两次，幽默地表达苏轼喜好作诗积习难改。