To be curious about something is to want to know all about it. If you're curious, you hope to find things out. And, something curious can be weird, strange, and interesting, making you wonder about it.
Cats are curious animals. They see or hear new things, and they want to know what's going on. They seem to ask, "What's this? What's that? Why?"
When you're curious about something, you can't wait to figure it out. You explore, you ask questions, you look things up, and you pay close attention. You've just got to know!