Revealing mistake: In the scene near the end when water is filling up the submarine, Kirk Douglas begins fighting with a member of the crew to escape. As Douglas hits him his false sideburn falls off and flies across the screen.
Revealing mistake: Kirk Douglas' stunt double is obvious during the scene of Nemo trying to drown him and his friends as they hold on to the dorsal.
Revealing mistake: The close ups of Ned Land and Conseil in their diving gear as they discover the sunken treasure were obviously filmed on a sound stage - there are no bubbles emanating from their helmets as shown in other actual underwater scenes.
Revealing mistake: When the shark attacks the divers, it is very obvious the shark is a puppet.
Answer: To see what kind of men they are, especially Ned Glass. They held on to the sub against the harshness of the ocean. They did not scream, cry, or beg for mercy.