Factual error: The giant squid's tentacles aren't shaped like ones in the real world are.
Factual error: The crew gasses out the ant hill by dropping chemical grenades into the hole. But there are two reality mistakes about the grenades: 1) chemical grenades do not explode; they spray their contents into the area; and 2) considering the size of the ants, the size of their nest must be gigantic, and therefore, it would take more than a hundred grenades to flood it completely with cyanide gas.
Factual error: Although the movie takes place in South America, the background jungle sounds include a bird called a Laughing Kookaburra. That bird is native to Australia and New Guinea, and not native to South America.