Brian's attempts to read the tracks in the sand leads to an important discovery when he realizes that his sanity is dependent upon his curiosity. He thinks that the very action of trying to make sense of his surroundings will prevent him from descending into utter despair. So, Brian's curiosity is inspired by his desire to survive.
But it was a mental thing. He had gotten depressed thinking about how they hadn't found him yet, and when he was busy and had something to do, the depression seemed to leave.
As Brian studies the tracks, he realizes that a water animal with a flat bottom and protruding side legs is responsible for the tracks. When he realizes that the claw-like tracks lead from the shore-line to a pile of sand, he starts to push aside the sand on top of the sand-pile. After some scraping and digging, he finds seventeen small turtle eggs buried four inches down. He reasons that the eggs must have been laid by a fresh-water turtle, likely a snapping turtle. His attempts to ascertain the source of his tracks are rewarded when he perseveres in his investigations.
Brian eats eleven of the eggs raw because he has no pans to cook the eggs in even though he has a fire back at his make-shift shelter. When he returns to his camp, he reburies the last six eggs near his sleeping area.