Summarize the incident involving the “large clump of rocks” that were moving.

As Salva and his uncle continued to walk through the desert, the waves of heat took over, making Salva feel as if everything was wobbling... out of sorts. As they continued to walk, Salva spotted what seemed to be a large clump of rocks moving in the distance, but as they moved closer he became aware that it wasn't rocks he was seeing... but rather, a group of people.