Factual error: The giant squid's tentacles aren't shaped like ones in the real world are.
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.
Audio problem: During the "Whale of a Tail" scene, there are several instances when Kirk Douglas' hands are away from the guitar strings, to ring the bell or twirl the guitar, yet the sound of the guitar strumming continues without missing a beat.
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.
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.
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.
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.
Audio problem: After the order "Beat to Quarters" is given, the Senior Petty Officer shouts orders, but no sound is heard from him. Further, the crew runs around shouting and no sound is heard from them.
Revealing mistake: When the shark attacks the divers, it is very obvious the shark is a puppet.
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.
Factual error: During the undersea trek, a nurse shark chases Ned and Conseil. Nurse sharks are actually pretty harmless and shy of divers.
Factual error: When they first arrive on the Nautilus, they look out the large porthole and see the crew on the bottom of the ocean burying one of the crew, but the ocean would be much deeper than that, since the Nautilus is at the surface.
