The highlands above the valley walls are called Harandra. Later Ransom learns that the Harandra is in fact the original surface of the planet. The hross tells Ransom that the Seroni live there and Ransom assumes they must be some sort of myth. Or then again, he thinks, could seroni be the plural of sorn? This has Ransom worried about whether the hrossa are merely domesticated animals of the sorn. This adds tension to the story and illustrates our own fallen paranoia.