The diver is shown walking ankle-deep into and out of the sacrificial pool several feet away from its "shore", but when he submerges he's suddenly in very deep water with no sign of a shallow underwater shelf upon which he could walk.
Abt 6:10 into the movie, when the scientist group are walking back to the grotto. Watch as their torch flames disappear as they pass to high up to the background matt screen.
As Arturo Dominici enters the jungle he walks past the camera and casts a shadow on the matt screen of the background.
Sometimes Max's face and hand look normal instead of scarred and bony.
When the police car drives up to Prof. Fielding's home, the car hits a motorcycle.
When the radio antennas and the radio operator are shown you can see a Norway flag in the background.