How to get the 3rd Dog Head Relief!

Overview

Well the puzzle in this guide might seem simple but i had a hard time finding the key to Dissection room so i made this guide for other players like myself!

Hot to get the key.

1.first of all you need to go to the Incinerator Room.
2.there is a note on the wall, above the sink.
3.Inspect the note which contain the puzzle! 3 A’s and the Handprint.
4.The key is in the very left Incinator but it’s locked! to open it, you need to open the very right Incinator…
and the one with the Handprint on it…
then the locked Incinator will open
and you can get the key to the Dissection Room!