Just before the title sequence, when the camera enters the lab, the cameraman can be seen reflected on the edge of the stainless steel worktable. He's wearing jeans.
When Jackson, Scott and Roland arrive at team one's dig site to find the corpses of team one in the excavation, the corpse on the left can be seen visibly breathing.
When the anaconda chases Amanda in her car through the forest, she looks in her rearview mirror, and the snake is slithering on a road. In the next shot, there is clearly no road, just the forest floor.