I wanted it to be a surprise, but my sister let the cat out of the bag.

我想给大家来个惊奇，可我妹妹却先说漏了嘴。

Their engagement was to be a secret but the ring on her finger let the cat out of the bag.

他们俩订婚原本想保密的，可是她手指上的戒指却把这个秘密泄露出来了。

I will give my mother a surprise on her birthday, but my father let the cat out of the bag.

我本来想在妈妈过生日的时候给她一个惊喜，没想到爸爸却泄露了秘密。

It's a secret so please don't let the cat out of the bag.

这是一个秘密，因此请不要泄露秘密。