Overview
Hollows are Leakborn creatures -- condensed Logic-stream energy given physical form. They appear as geometric shapes: cubes, spheres, tetrahedra, and occasionally shapes that don't correspond to any human geometry. Made of something that looks like glass but isn't -- solidified pattern. They glow from within with a cold, blue-white light.
They have been found in Thornwood's deepest basement levels, in mathematical archives, and occasionally floating through the library at 3 a.m.
Behavior
They solve things. Leave a mathematical proof near a Hollow and it will rotate to show you the error. Leave a broken mechanism near one and it will hum at the precise frequency needed to identify the fault. They are not helpful in any intentional sense -- they just ARE solutions, the way a river IS downhill.
Significance
Alice is the first student to realize the Hollows are communicating with each other. Their harmonic tones form a language. She begins translating. What they are saying is a continuous, running calculation of the Loom's structural integrity.
When the tones change pitch, Alice knows the Loom has cracked further. Their math is perfect. Their conclusion is unanimous: the break is inevitable. The only variable is when.