When Frenchy takes Capt Morgan to the cellar to remove a bullet, Frenchy unlocks the cellar door and promptly relocks it after they enter the cellar. A few minutes later, Slim comes down the stairs in the cellar with the first aid kit and the hot water. Frenchy has been in the room with the wounded man all this time and couldn't have unlocked the cellar door.
When Harry Morgan is sitting in the bar, the bottle on his table moves around and disappears between shots.
When Steve and Slim leave the room to confront Johnson with the wallet, as they turn the corner Slim is wearing white flats. After the bar room shooting and questioning at police headquarters, she walks out in black heels.
Just before Harry dumps water on Eddie's head, we see the scene from the side, and Eddie's mouth is open. It then cuts to an overhead shot and Eddie's mouth is closed.
(at around 1h 39 mins) When Slim walks over to the piano to say goodbye to Cricket there is a crowd gathered around the piano watching them but as the scene goes through various edits, the make-up of the crowd and the positioning of some of the people in the crowd keep changing.
While on the boat, and just after the exchange of fire, Harry tells Eddie, who is at the helm, to steer the boat at "one sixty." A boat captain would pronounce this "one-six-zero" to avoid confusion with "one sixteen" (pronounced "one-one-six").
When Harry calculates how much Mr. Johnson, his fishing customer, owes him, he says more than once that it is 16 days x $35/day, + $275 for the rod and reel he lost. That totals $835. When he has Johnson's wallet he says Johnson owed him $825 (more than once). Harry calculates the amount and says, "Now you got a little credit so that'll be 825". The difference between 835 and 825 is, presumably, "...a little credit."
When Morgan throws water at Eddie, the bucket is obviously empty - noticeable both in the way it's handled and in a momentary glimpse of the insides before the camera cuts to Eddie.
Just before Eddy is slapped, supposedly unexpectedly, by Steve (c. 49 minutes), the left side of his face tenses up in anticipation of the blow.
At the dock the line where the water meets the fake scenery is very evident.
When the patrol boat is firing at Morgan's boat, the machine gun is not recoiling, the bolt is not moving, nor is there any gun smoke. With this type of MG, the bolt would recoil after every fired cartridge and would cause the whole gun to have some recoil effect. The gunner was just standing there; he would have to move his fingers or thumbs to fire the gun.
When Harry gives Johnson the wallet that Slim lifted, she's eager to light his cigarette, holding a match on the matchbox ready to strike it on cue.
At 00:47:32 when Marie first notices Harry entering the hotel she looks to her right, but actually he has entered to her left and walks up to her left side.
The map of the Caribbean that is under and after the opening titles is inaccurate. The map shows Martinique as about 200 miles south of Puerto Rico, whereas it is actually about 380 miles southeast of Puerto Rico. It shows Martinique as bigger than Puerto Rico when it is actually about 1/8 as big and much skinnier. It also shows Martinique's western tip pointing between the Yucatan peninsula and Cuba, when it is more like a northern tip that points about 100 miles east of Puerto Rico.
The musical group sings in Spanish even though they're in a French province.
Early in the film, Harry must get a permit to exit the port to take Johnson fishing. When he goes to get the smuggled freedom fighter and his wife, Harry has no problem leaving or reentering port after the rendezvous.
The microphone casts a shadow to the left of the door when both Slim and Madame de Bursac leave Harry's room.
At about 00:14:35 when Frenchy says "But they are coming to see you tonight" the boom mic shadow moves back and forth across the far wall.
Harry at first misses grabbing the table to overturn it.