This can only be done in the Banned Footage Vol. 1: Bedroom DLC. After Marguerite brings the second meal to you and leaves, get out of the bed and use the fork on the food she brought. Inside the food you will find a dead rat. Next to the table with the clock, you can find the second dead rat on the ground behind some debris. The final dead art is located behind the password locked door. The password is snake, maple leaf, apple. Head inside and grab the last dead rat from the top of the bookcase.
Here is a video guide with English commentary!
Here is a playlist of for this game!
https://www.youtube.com/playlist?list=PL-HeW6XkKdUKUtj7CV_kW...