Why do most iguanas just ... sit there? 96% of the day, in fact! Well, they're herbivores, which is very rare in the lizard world. Digestion can only occur when that cold-blooded body heats up to 40 degrees Celsius. When they do move, however, things get interesting. From escaping predators to mating behaviors, the iguana's true intelligence is on full display. Ask any pet owner and you'll hear some lively tales of the costly upkeep and close personal bond the iguana forms with its human host.