While we’re talking about cats:
Je donne ma langue au chat.
I don’t know, I give up.
But wait, you say. I see a “chat” in there. Didn’t tell me that’s a cat? Where’s the cat?
Aha! Another case of what-you-see-is-NOT-what-you-get, or WYSINWYG for you techies. If we translate this idiom literally, we get “I give my tongue to the cat.” No one knows why. It’s just what you say in French when you give up trying to guess a riddle.
Interestingly, we have a kind of companion phrase in English: Cat got your tongue? In French, you are admitting that you have nothing to say. In English, someone else is teasing you about not being able to speak.
What cats have to do with not speaking is another matter. For that matter, what do cats (and dogs) have to do with heavy downpours of rain? That’s the fun of idioms. You never know what you’re going to get, but it’s not likely to match up with whatever you are accustomed to saying!