Rats are the secondary antagonists in Layers of Fear. They appear often in various rooms, and are the cause of at least one instance of the player blacking out and returning to the Circle. They are the unwitting subjects of the Rat Scrawlings.
Reality or Hallucination? Edit
A big question throughout the game regards the existence of the rats. In Iteration 0, a letter is found from an extermination company that claims that after a thorough search of the house, no evidence of rats was found. Although they appear often, they may be a form of hallucination. The continuous strangeness found in the rat scrawlings supports this theory.