Revealing mistakes: On top of the ruins there is an opening with a rope in which people can lower others by turning a wheel. When one of the characters is going down into the ruins, the camera changes quickly between the person going down into the ruins and the characters lowering the rope. Even though they are lowering a person into the ruins, they are actually twisting the wheel the wrong way, which shows the rope moving up, as if they are taking someone out of the ruins.
Revealing mistakes: The rope for the descent into the ruins changes lengths.
Incorrectly regarded as goofs: While on top of the ruins, a bottle containing an amber colored liquid is shown several times. At one or two points the label is visible, saying "Blanco tequila." Blanco (white) tequila is completely colorless. However the liquid may not be tequila. In the novel the characters urinate in a bottle anticipating that they may have to drink their own urine. The bottle of tequila may be this bottle.
Continuity: When inside the ruins, Amy clearly loses her glasses while trying to escape from the vines. She and Stacy are pulled out of the ruins and she has no glasses. Two scenes later she is wearing her glasses again, then every scene after that she has no glasses, through the end of the film.