A Yellow Spotted Lizard is a poisonous creature that inhabits the arid wasteland of Green Lake. Each lizard has yellow eyes, black teeth, red-rimmed eyelids, a milky white tongue, greenish skin, and 11 spots - however if you get close enough to count the spots, you're probably dead. A Yellow Spotted Lizard is more venomous than a rattlesnake or a scorpion. One bite can cause a slow painful death - always. One thing that saved Stanley Yelnats IV and Zero (Hector Zeroni) was that after eating a large amount of onions - Sam used onions as a Yellow Spotted Lizard repellent - they smelled of onions, and that prevented the lizards from biting them. "Yellow Spotted Lizards hate onions".
The actual lizards used in the film were actually harmless Bearded Dragons. Nine Bearded Dragon lizards were on call for the parts of the lizards in the film. A non-toxic children's finger paint was used on the lizards to make them appear bright in color. Computers helped create some of the lizard action and production created fake life-like lizards for some of the other scenes.