Okay, imagine you're in a school with your friends. Imagine you're playing a game of tag and you're it. You're chasing your friends and you're having a lot of fun, but then suddenly you trip and fall. Ouch! You hurt your arm really badly and it's hard for you to move it.
Now imagine you have to go to a special doctor who knows how to fix arms. This doctor wants to try a new medicine to help your arm get better, but they can't just give it to you without checking if it's safe.
This is what a "Riom Trial" is like. It's a special test that doctors do to make sure new medicines are safe before they give them to people. The doctors get a bunch of kids with hurt arms, just like you in the schoolyard, and they split them up into two groups.
One group gets the new medicine, and the other group gets a special sugar pill that doesn't do anything. This is called the "placebo" group. The doctors watch both groups very carefully to see if the new medicine helps the kids' arms get better faster or not.
If lots of kids in the medicine group get better faster than the kids in the sugar pill group, the doctors can start giving the new medicine to other kids to help them too.
So, there you have it! A Riom Trial is a special test that lets doctors try out new medicine to see if it's safe and works. Just like you tag your friends at school, doctors tag kid's arms to help make them better!