There's a point in A Plague Tale: Requiem where Arnaud falls into a rats' nest and needs your help to get out safely. The area is pretty dark and the situation looks dire so you might be wondering how you're supposed to open the way for him.
Much like saving the herbalist, it's pretty tricky to figure out what you're supposed to do—especially when there are so many rats nearby waiting for you to make a mistake—so I'll explain everything you need to know in this guide. Here's how to open the way for Arnaud in A Plague Tale: Requiem.
A Plague Tale: Requiem Arnaud: How to open the way
The incident in question happens in Chapter 7 of A Plague Tale: Requiem. Amicia and Hugo have reluctantly teamed up with Arnaud and are making their way through a cave when Arnaud falls from a narrow ledge and lands among the rats below. The first thing you should do is light the brazier close to him with an Ignifer and your sling.
That's Arnaud safe for now but you need to find a way to get him out of there. Luckily, Hugo will point out the yellow crystals down in the rats' nest. These are Episanguis, and Amicia will ask Arnaud to throw her one. Once you have it in your possession you can craft Odoris which will draw the rats' attention for a short time. Fire the Odoris onto the ground below, attracting the rats and leaving enough room for Arnaud to get past and to the relative safety of a ledge at the back of the cavern.
Arnaud should be standing next to a crank. Tell him to use it, and a wooden board attached to a chain will rise nearby. Use another Odoris bolt on the wooden board, then release the crank and the rats will move again. Arnaud should now be able to move past them and rejoin you. Good job.