Went Out Like Lights (Simile)
When Penny and Primrose are deep in the forest for the first time, the normal sounds and scents of the forest are suddenly replaced by the rumbling and putrid smell of the creature approaching them. Byatt writes, "The new, ordinary forest smells and sounds, of leaves and humus, fur and feathers, so to speak, went out like lights as the atmosphere of the thing preceded it." In this simile, Byatt emphasizes the suddenness of the shift in atmosphere by comparing the disappearance of the forest scents and sounds to lights being extinguished.
Light Cobweb Voice (Metaphor)
When Penny and Primrose finally discuss, several decades later, what they saw in the forest, Primrose speaks "in a light, light, cobweb voice." In this metaphor, Byatt likens Primrose's voice to a spider's web to emphasize its delicate, haunted quality. The effect is that the conversation takes on a darker, more eerie tone.
Like a Tapeworm in Your Gut (Simile)
When Penny and Primrose discuss the lasting impact of seeing the Thing in the forest, Primrose guesses correctly that Penny, like her, has never spoken about it to anyone else. Primrose says, "I didn't speak. But it stuck in my mind like a tapeworm in your gut. I think it did me no good." In this simile, Primrose emphasizes how the memory of the Thing has inhabited her mind by comparing it to a physical parasite that lives inside the gut.