Why did Stanley nearly gag on the cereal in Holes?
Stanley almost gags on the cereal because it is too sweet and he has eaten nothing but onions for a week.
Stanley and Zero escape Camp Green Lake and run off into the desert. There is no actual lake, so it is very dangerous. Fortunately, Stanley finds a supply of onions left from Kissing Kate Barlow’s day, and the boys are able to survive on those.
The boys decide to look for Kate Barlow’s treasure in the place that Stanley found the lipstick tube. Stanley and Zero return to the camp and hide out in the holes, waiting for everyone to fall asleep. They make sure to get some water. Zero brings Stanley cereal.
Stanley carefully poured some cereal into his mouth. He didn't want to put his dirty hands inside the box. He nearly gagged on the ultra-sweet taste. They were sugar-frosted flakes, and after eating nothing but onions for more than a week, he had trouble adjusting to the flavor. (Ch. 44)
The boys keep digging through the night, and when they find the treasure the warden is there. The yellow-spotted lizards are there too. The lizards are deadly, but it turns out they do not like onions. All of the onions that the boys have been eating serve as protection from them. They are able to wait out the lizards, who leave when the sun comes up.
Mr. Sir tells Stanley that he was supposed to be released.
"Hey, Caveman, guess what?" said Mr. Sir. "You're innocent, after all. I thought you'd like to know that. Your lawyer came to get you yesterday. Too bad you weren't here." (Ch. 46)
In the end, Stanley does get to go home. The lawyer and the Attorney General shut everything down. Stanley ended the curse, rescued Zero, survived the lizards, and got out of Camp Green Lake.