He can't keep a secret.
You've got a big mouth!
I don't have the guts to say that to my boss. *guts表示“勇气”
A little bird told me that today is your birthday. *听小道消息说、听说
Wait. Who told you? 喂!谁告诉你的?
I heard it through the grapevine. *grapevine原为“葡萄藤，此表示谣言,传闻
I just overheard it.
I didn't say anything.
I kept my mouth shut.
I didn't let the cat out of the bag. *表示“没有泄露秘密”的固定说法。
It was a slip of the tongue.无意中说漏了嘴
Really? Didn't she know about it?
I spilled the beans. 我泄露了秘密。
I stuck my foot in my mouth.
I won't say a word.
Mum's the word. 我什么都不说
I won't say anything.
My lips are sealed. 我的嘴很紧。