Other mistake: When Carl and David go down in the submarine, they come across the sunken plane that they crashed in. As they approach the plane, it shows that the it is clearly on the right side of the sub as they go from the tail to the prop. When it cuts back to them in the sub, they are looking to the left. A cut back to the plane still shows that it could only be on the right. Carl then looks out the left port hole of the sub and it clearly shows them going by the plane from prop to tail.
Other mistake: The caverns of the so-called World Beneath would be flooded if they were below sea level due to the principle of communicating vessels. There is no explanation why the water stops rising up at the two 'wells' in the caverns.
