Goofs

The young Benjamin speaks with a British accent, but his adult self speaks with an American one.

About 52 minutes into the movie, Ben (Tyrone Power) gets out of the water to talk to Eve (Gene Tierney) and places his knife and an oyster shell on the rocks. Eve dives in the water and Ben follows without having retrieved his knife but in the next scene, he is shown underwater chasing Eve with the knife between his teeth.

When Bristol Isabel (the doxie) leaves to run Ben's errands, she locks the door. When she returns, she is seen to rush right in without having unlocked it.

Isabel, Ben's cousin, should not have been alone with him in the stables. In the time period this is set (late 18th century), a girl of her class would not have been alone out of doors for any great length of time; a chaperone, maid, or nanny would have accompanied her everywhere but especially if men were near.

British judges do not use gavels and never have (other than in American-made films).

When Caleb puts his magnets near the compass, he changes the heading from NNW to NW. To correct to the new (false) heading, Ben moves the ship to starboard, or northward, meaning that they are really going true north. However, when Caleb explains his interest in getting to the islands, he says they are southwest of where the ship is. He has moved the ship farther from where it should be to reach the islands.

The ship sails the Atlantic from London headed for Brazil. Caleb (John Carradine) causes Ben to steer off course and they end up in the South Seas.

Months pass on the island, yet Caleb's beard never grows longer or more shaggy (nor does Ben's grow at all, although it's possible that he shaves), and Caleb's Western-style clothing does not become ragged.

George Sanders's trousers have a very clear (and shiny) zipper up the back in the fight in his daughter's bedroom.