let the cat out of the bag 露马脚

“露马脚”是一个汉语词语，字面意思是“show one's hoof”，用于比喻“不小心暴露了隐藏的真相（to reveal a hidden truth carelessly or by mistake），或现原形（give oneself away）”，与英文习语“let the cat out of the bag”意思相近。

例句：

这个小偷因大量花钱而露了马脚。

The thief gave himself away by spending so much money.

他无意中露出了马脚。

He betrayed himself without meaning to.