On this page of our guide to Layers of Fear 2 we have described in detail the kettle riddle, which has to be solved during the first act of the game. You will learn where to find the three items that should be thrown into the kettle.
You will find the kettle immediately after using the key to unlock the entrance to the kitchen. You can leave the kettle be for the time being. Your task is to find three items to throw into the pot and cook them.
Go to the next area. One of the mannequins is sitting near the cross. You will find here the brain, i.e. the first of the three "ingredients" and put into the pot.
Inspect the left passage and, after watching a short scene with the dummy, lift the limb.
Return to the central room and inspect the right passage. Also, you need to watch the animation of the dummy. Only then take the mechanical heart.
Return with all the components to the kettle and throw them one by one.
In place with the mannequin sitting next to the cross, a new passage will open.