Continuity mistake: When Ned Land dives into the ocean to save Nemo from the giant squid, his knife is in his hand. After Ned reaches Nemo, he then draws the knife from its sheath.
Continuity mistake: Before the Nautilus rams the munitions ship emerging from the harbor, there is a land mass on the Nautilus' starboard side. After the Nautilus attains collision speed, the oncoming shot of the Nautilus shows no land mass.
Continuity mistake: In the opening scene, as the first Nautilus attack takes place, there is a moment, where the camera shows the Nautilus from the top and there is green light coming out of the back, as it was made out of glass. But the top of the Nautilus is made from iron.
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.