 Why did Loy Chuk's people live underground?
Loy Chuk had flown his geological expedition out from the far lowlands to the east, out from the city of Kar-Rah. Loy Chuk and his fellow workers were gathered, tense and gleeful, around the things their digging had exposed to the daylight. Medical and biological sciences were far advanced among Loy Chuk's kind. Loy Chuk's people had built their homes mostly underground, since the beginning of their foggy evolution. The mummy was taken to Loy Chuk's laboratory, a short distance below the surface. He did not know that in the latter, his language, taken from his own revitalized mind, was recorded, and that Loy Chuk had only to press certain buttons to make the instrument express his thoughts in common, long-dead English.
 The temperature above ground at night is very cold.
 Subterranean passages protect against desert sand storms.  Subterranean passages protect against larger predators.  Loy Chuk comes from a rodent species. Rodents usually live in underground burrows.  The temperature above ground at night is very cold.