During the Chapter VII of A Plague Tale: Innocence, you will have to get rid of rats in Chateau d'Ombrage. You can do that by moving mechanisms in the right order. The next section will tell you how to do this.
You can find the first hearth right after you enter inside - Set it on fire and move towards the ladder. Also, set fire to the adjacent hearth. Then, take a stick and set it on fire. Thanks to this, you go between two sources of light and reach the ladder.
A mechanism is at its top. Turn it all the way - the rats will fall into the moat, and Melie will be able to pass. Then, lower the bridge.
Go to the next mechanism. Light the hearth located directly below you and go down - you need to be within its radius. Tell Melie to move the mechanism and follow the light. Next, light another hearth and climb the shelf. There, move the light source as far as you can.
Wait until the mechanism released by Melie passes you and then go back to the starting hearth. Your friend will be waiting there. Climb to another mechanism. Lower the bridge and return to the lever. Light another movable hearth and go down to the light source.
You will get to the next hearth. Light it and take a stick. You will use it to get to the ladder. Set the torch on fire to reach that place. Move the hearth. Melie will release the mechanism - it will make the rats run.
Lastly, move the exterior mechanism - the one you have moved earlier. It will push all the rats into the moat.