Onions symbolize a positive and healing factor in the novel. Sam, a character of good will and intelligence, loves onions and helps to cure sick people with the onion remedies that he makes. The onions allow Stanley and Zero to regain their health and rest before attempting to break free of the oppression of Camp Green Lake. The onions also help Stanley and Zero avoid bites from the deadly yellow- spotted lizards that frequent Camp Green Lake.
Yellow-spotted lizards represent the deadly aspects of Camp Green Lake. They invaded the area after the life-giving lake dried up and they present a deadly threat to all humans at the camp. It was a yellow-spotted lizard that killed Kate Barlow and it is yellow-spotted lizards that threaten Stanley and Zero while they are digging for Stanley's great-grandfather's suitcase. The reason Stanley and Zero survive is because they have eaten so many onions (a positive and life-affirming symbol) that the lizards, who do not like onion blood, do not wish to bite them.