let the cat out of the bag: 比喻无意中泄露秘密，说漏了嘴。
我刚刚对你说的是机密，别说漏了嘴：
What I told you just now is a top secret information. Don’t let the cat out of the bag.
别把个人的秘密告诉他，他经常说漏嘴：
Don’t tell your personal secrets to him. He always lets the cat out of the bag.
松浦弥太——《今天也要用心过生活》
