The Bone Saw is an optional tool item in Amnesia: The Dark Descent, found in the Nave. The collection and use of the Saw are completely optional, as it will not stop the player from reaching the end of the game one way or another (but can affect the outcome of which ending the player gets). It can be used to cut off Agrippa's head after feeding him Weyer's Tonic.
Description[]
The Bone Saw is found in a room left of Agrippa in the Nave. When Daniel first enters this area, the aforementioned room in the Nave is inaccessible - being blocked by a wall. It is not until Daniel returns to the Nave from the Cells that this item becomes reachable. Upon returning here, the room with the Bone Saw is now accessible due to the blocked wall being destroyed by The Shadow.
Once the Bone Saw is collected, it can only be used to cut off Agrippa's head after he's fed Weyer's Tonic. If Daniel attempts to use the Saw on Agrippa before he's fed the tonic, he will say, "Don't get ahead of yourself. First, we need the tonic."
