If you tell about something that was supposed to be a secret, we say you let the cat out of the bag.

VOA: special.2009.09.27

Takes one to know one so the biologist must himself be a cat.

不过同类互知,那么这个生物学家他自己必须是猫

耶鲁公开课 - 死亡课程节选

So on the left hand side of this particular languages environment I have some puzzle pieces and they are shaped and colored ; in a manner that hints out their functionality; any blocks that tell the Cat as we'll see in a moment, what to do something happen to be orange.

在这个程序语言界面的左手边有一些拼图,他们的形状和颜色代表他们的功能,我们马上就能看到;,任何一个给计算机发出指令的图块，都是橙色的。

哈佛公开课 - 计算机科学课程节选