Final answer:
The provided excerpts do not contain information about a character named Salva or an event involving crying while crossing the Akobo desert; therefore, an accurate answer cannot be given based on the information provided.
Step-by-step explanation:
The question seems to reference a specific story or book, which is not clearly identified in the provided excerpts. However, none of the excerpts provided directly relate to a character named Salva nor do they describe a scene where a character breaks down crying while crossing the Akobo desert. Therefore, without the context of which book or story these excerpts are from, and without any excerpt mentioning Salva's experience in the Akobo desert, it is not possible to accurately determine what caused Salva to break down and cry in that particular scenario.