Revealing mistake: The Acheron fires many devastating blows on the Surprise and the effect is visible in close-ups and a wide shot. However, after Mr. Mowett yells, "Relieving-tackles on the tiller! You men collect the wounded!" there is another wide shot of the Acheron in the foreground and Surprise in the distance. In this shot Surprise has NO damage whatsoever! (00:11:00)
Revealing mistake: After a close-up of the drawing of one-armed Lord Nelson, Killick opens the lid of the steaming food for Jack in a close-up, just before Killick says, "Oh, here we go again. Scrape, scrape, screech, screech." Later, after Pullings takes command of Acheron, Jack tunes up his violin and Killick says, "Here we go again," in another close-up of the steaming food for Jack. Every detail of the food shown in both close-ups is exactly the same - obviously shot at the same time. (00:26:25 - 02:05:20)
Revealing mistake: When the Surprise is disguised as a whaler, it burns smoke from the front end of the ship to make it look as though it is making whale oil. When it is chased by the French ship the smoke blows back over the ship. As they are sailing ships the wind is behind them which means the smoke should blow forward. (01:44:45)
Revealing mistake: The characteristics of the scarring on Jack's left earlobe changes in quite a few shots. The scar, in the shape of the letter Y, over Jack's right eye changes its angles and as for the scar at his hairline, the upper and lower line switch off being longer in length throughout the film. (00:18:35 - 00:33:00)
Revealing mistake: During the scenes when Jack and Stephen are playing their instruments, it can be concluded that they are not genuinely playing. This is most noticeable in their last scene, when strumming. You will notice that they will be strumming when no music is audible. (02:07:35)
Revealing mistake: After the Captain cuts loose the man who fell overboard in the storm, there is a scene where the men sit around the big table and sing a song. During the song, the camera pans in a sweeping shot around the table. Watch closely as it comes around to the near side of the table, and you'll see the camera's view quickly jolt, as if it lightly smacked against something by accident during the filming.
Chosen answer: They stop singing because they hear Hollom joining in. There are very strict ranks in the Navy, and Hollom singing with the lower crew dissipates these ranks, which is undesirable. That Hollom sings with the crew is frowned upon by the captain, as can be seen by his serious/agitated reaction after Stephen mentions that Hollom has such a clear voice.