As God's Thumb looms overhead, Stanley feels afraid. He fears that if there's no water up there, he and Zero will have nothing. The land gradually becomes steeper and steeper, forcing Stanley and Zero to zigzag up the mountain. They begin to see weeds, which get thicker the higher they climb. The sun begins to set and gnats attempt to land on the boys. Zero and Stanley resume their spelling game until Zero vomits. Stanley realizes that they must be close to water if there are weeds and bugs, and he tells Zero this. Zero smiles, flashes Stanley a thumbs-up, and collapses. He doesn't move when Stanley shakes him.
When Stanley is able to deduce that there must be water nearby, it shows that he's developing more of an appreciation for the natural world and doesn't necessarily see it as his sworn enemy anymore. This suggests that he's changing to become more like Sam in how he views the natural world; it is something benevolent, especially now that he's following nature's signs towards God's Thumb.