Final answer:
The question appears to be regarding a group of rats from a literary narrative who leave some members behind as they escape a lethal threat. This plot element highlights themes of sacrifice and strategic survival often found in literature.
Step-by-step explanation:
The narrative in question seems to be describing a scenario where a group of rats decide to leave some of their members behind as they move to a new location, Thorn Valley, to escape the threat of being gassed in their current burrow. There could be various reasons for this decision, which may include strategic purposes such as safeguarding the route to the new dwelling, or a sacrificial maneuver to ensure the majority can escape. Such a plot element is typical in stories where characters face peril and must make tough choices for the greater good.
In a broader context, this scenario is reflective of themes often explored in literature where communities face existential threats and must strategize for survival, sometimes at the cost of sacrifices. The decision to leave some behind might be part of a larger narrative device, emphasizing the stakes involved and the grave nature of their situation.