During the man overboard warning, Kelly's hair is curly while she dresses, much flatter when on deck, and curlier again when she dusts the gun for fingerprints.
In the beginning the cruise ship has two funnels, then later it has three.
After seeing a man's shadow from around a corner, Jill discovers Fred Couper's dead body suspended by a rope. When the corpse is first shown, the hands are swinging back and forth, despite the fact it was in an interior hallway with no wind to make the body move.
The Angels claim that the each will cover a specific class with Sabrina taking Third Class, Kelley taking Second, and Jill taking First. The three class system of accommodations was used in the ocean liner era. Modern cruise ships are not divided into classes. Patrons of cruise ships usually pay different fares based on the type of rooms they want yet most of the ships public spaces are open to all those passengers aboard the ship.
The purser is wearing 4 stripes on his shoulderboard. That is a captain's insignia. He should be wearing one stripe, two at most.
When the Angels and Bosley were interrogating Harry Dana, there were never any "horizons" seen out the portals behind Sabrina and Bosley.
When the dummy dressed as Bosley falls from the crow's nest, the Angels run the wrong way. They end up closer to the dummy than if they had stayed in place.
The shadow cast by Fred Couper's corpse is on the wrong wall, based on the light source. Additionally, the rope that holds him up casts no shadow of its own.
After being shot at, while the Angels are sidling along a wall and running up some stairs there are a number of crew/equipment shadows that move in the foreground.
When Kelly goes up through the access door the hand of a crew member can be seen on the right hand side helping to pull it away from the opening.
Kelly is hidden from Harry Dana's view when he attempts to destroy fingerprint evidence from the "Live Steam" valve handle. Yet, when he closes the access door, he leaves even more fingerprints on the door, twice. It is unclear if Kelly ever noted this fact; she never mentioned it, and, no one ever "dusted" those prints.
In the evening, in one shot of the ship's port side, the flags near the rear of the ship are low. The top flag is even with the rear smoke stack. Moments later, the flags are much higher.