On landing in the crater, Maggie stands before a threatening carnivorous plant. Later in the film, after Maggie's clothing has been torn and her blouse has become sleeveless, she and Hal flee a T-Rex. She again nears the plant, but her clothing is complete and spotless, just as in the earlier shot.
As Dr. Carl is kidnapping Maggie and bringing her to his cave for the first time, we see a long shot of the mouth of the cave - look close and you can see the rubber raft that Maggie will row there later in the film, tied up next to Dr. Carl's reed boat. At this point the rubber boat should be back at camp, with the crew.
Cdr. Roberts sends Steve and Maggie back to the helicopter when they are faced with the T-Rex for the first time. In the next shot with the T-Rex in the foreground, one can see Steve and Maggie hurrying off. However, it is at an unnaturally fast speed, showing that the film has been sped up at this point.
The four helicopter occupants conduct a normal-volume conversation in flight. The engine noise would make that impossible.
The big aquatic monster swims by using its lateral paddles/limbs alternately. No aquatic animal swims like that.
When Hunter stuffs his first fiery pole into the monster's mouth. the action of the flames shows that the film is run backwards briefly at one point.
When the tarsier mammal is captured by the plant, the wires controlling the plant's tentacles are clearly visible.
The film is set in Antarctica, yet at the end of the film, when the occupants of the helicopter are rescued by the naval ship, it is clear that they are nowhere near ice-choked Antarctic waters. They should have been frozen solid in their threadbare attire once thrown into the water.
In the helicopter, Roberts comments that a group of Adelie penguins is 'all female'. Male and female of the species do not have obvious morphological differences that permit sexing in the field.
On the ship, reference is made to travelling through 700 miles of ice. There is nowhere around Antarctica where there is ever such an extent of continuous navigable floating ice.
As stated in the pre-expedition lecture, Admiral Richard Byrd did make discoveries in Antarctica as part of Operation Highjump (1946-7), but they did not include an 'ice-free warm-water region' - because there isn't one.