人心隔肚皮

[成语]
rén xīn gé dù pí

[含义]
谓人的心思难以猜测。

[来源]
清·钱彩《说岳全传》第四回：“虎豹不堪骑，人心隔肚皮。休将心腹事，说与结交知”

[例句]
可是，～，有些事儿，哪能想到呢。 端木蕻良《曹雪芹》


[英文]
different hearts in different breastsIts hard to tell whats going on in the minds of other people. or People should always be on guard against one another.