There is a moment as heatstroke sets in when the body, no longer able to cool itself, stops sweating. Joey Azuela remembers it well.
"My body felt hot, like, in a different way," he says. "It was like a 'I'm cooking' hot."
Three summers ago, Azuela, then 14, and his father were hiking a trail in one of Phoenix's rugged desert preserves. It was not an unusually hot day for Phoenix, and they had gotten a later start than usual. By the time they reached the top, Azuela was weak and nauseous. They had run out of water.