Okay kiddo, do you know what a whip is? It's a long, thin piece of string or leather that people use to make a loud cracking sound or to make animals move faster.
Well, the cat o' nine tails is a special kind of whip that has nine tails instead of one. Each tail is like a mini whip on its own. It was used a long time ago on ships and in prisons to punish people who did something wrong.
When someone got hit with the cat o' nine tails, it would hurt a lot and sometimes even leave cuts on their skin. That's why it was a really scary thing for people to face.
But don't worry, kiddo. Nowadays, we don't use things like the cat o' nine tails anymore because we know that hurting people is not the right way to solve problems. We believe in being kind and treating others with respect.