The carved stones are a symbol representing the intrusion of an alien, hostile reality into the human world. They are the first definitive evidence for Mouse that the supernatural horrors described in Cotgrave’s journal are real, functioning as the primary landmarks of the impossible hill that appears behind her grandmother’s house. This connection to a landscape that defies cartography and logic makes the stones central to the theme of The Thin Veil Between Rationality and Nightmare. That one of them is present in the house’s garden signifies that this alien reality is actively encroaching upon the mundane.

The horror of the stones stems partly from their carvings, which seem to shift as living creatures would, destabilizing the boundary between animate and inanimate objects. Foxy’s speculations on their origin underscore this point: “Maybe they grew […] Ever think of that, eh?” (105). Her question reframes them as a monstrous, geological life form, further cementing their status as symbols of an unnatural, invasive world. Moreover, the carvings have a hypnotic effect on the observer, giving them an agency that mere stones lack. Cotgrave’s journal reveals their dangerous influence through a recurring litany: “I made faces like the faces on the rocks, and I twisted myself about like the twisted ones” (31). This phrase, which originates in the Green Book, demonstrates that the stones exert a memetic power, compelling the viewer to internalize their twisted forms. The stones thus collapse the boundary between the observer and the observed—another way in which they challenge accepted reality. That the white monolith can impregnate women who encounter it marks the culmination of the stones’ various “violations” of the natural order: It is a biological impossibility that Anna nevertheless confirms to be true.