Today’s saying is:
Let the cat out of the bag.
It means:
To tell a secret or something that shouldn’t have been told, sometimes by mistake.
Examples of how to use it:
I’m going to tell you what I bought your mother for her birthday, but I don’t want you to let the cat out of the bag before the party.
Our boss was going to surprise us with $1,000 bonuses at Christmas, but one of our co-workers had already let the cat out of the bag, and the boss was disappointed that it wasn’t such a big surprise.
Sue didn’t know that she was letting the cat out of the bag when she told her husband that his friend Bob was leaving his wife.