• A rat brain in the player's inventory.
  • A rat brain on the ground.
The rat brain is an item which rarely drops from rats in The Maze. Lysis will use it and a Potion of Perception to craft a Potion of Comprehension.

Lysis will pay 14 gold for the brain and sell it for 50.

It is actually has quite a high demand, because of the comprehension potion's effects.