Continuity mistake: Lieutenant Carlsen says, "Get that light off me" as the PBR approaches the shore. Lance, sitting at the front machine gun, starts to move the spotlight before the lieutenant says anything then in the next shot the spotlight is already facing him. (01:41:40)
Continuity mistake: The lights on the Do Lung Bridge keep changing between shots. There are many more burned out light bulbs in the shot of Captain Willard and Lance as they leave the boat then there are when we first see the bridge or when the bridge is in the background as they walk past it. (01:42:15)
Continuity mistake: We see a close-up of Lance's face as he talks to Chef on the front of the boat at they approach the Do Lung Bridge. The camouflage makeup around his chin and left cheek is different as he walks across the bridge with Captain Willard. (01:42:35)
Continuity mistake: After Lance and Captain Willard return to the boat Chief Phillips says, "which way captain". As the captain sits on the front of the boat look closely at his tee shirt, he has something underneath resembling a large newspaper or package. When he takes his tee shirt off there's nothing under there except his dog tags. (01:47:55)
Continuity mistake: Before they leave the Do Lung Bridge Captain Willard yells to Chief Phillips, "Just get us up river". When he does this he's sitting down but in the next shot as the boat pulls out he's standing up. (01:48:15)
Continuity mistake: When they leave there are two fires on the Do Lung Bridge as Clean looks on manning the rear machine gun. In the next shot there is only one fire on the bridge. (01:48:45)
Continuity mistake: When they leave the Do Lung Bridge the flag is visible on the roof of the boat, but several seconds later at the beginning of the next scene, it's gone. (01:48:45)
Continuity mistake: As they all read their mail from home Lance ignites a canister of purple smoke and it's sunset. In the next shot of Clean grabbing his tape recorder it's the afternoon and the sun isn't even shining. (01:50:55)
Continuity mistake: As Clean says, "I gotta tape from my mom," we see a rope tied around the cleat on the starboard side of the boat. He doesn't go near the cleat as he listens to the tape but the next time we see this spot, right when the attacks starts, the rope is gone. (01:51:00)
Continuity mistake: When Clean sits down in the back of the boat and opens up the tape from his mom, notice the order of the bullets in the machine gun to the right of the screen. When we first see them they're all packed in order, three shots later as he reads the letter they're uneven though no one has touched them. (01:51:00)
Continuity mistake: When he first opens the package from his mom Clean is holding a brown envelope with a cassette tape in it. Three shots later as he reads the letter from his mom and listens to the tape, the package has changed to a white carton. (01:51:05)
Continuity mistake: After leaving the Do Lung Bridge everyone sits around reading their mail from home. Lance takes the canister of purple smoke and proceeds to throw it overboard as he says, "Hot potato. Hot potato." In the next shot he has the canister in his hand again. (01:51:15)
Continuity mistake: As they all sit on the boat and read their letters from home Lance dances around with the purple smoke canister. Look closely as the red Vietnamese banner on the shoreline disappears between shots. (01:51:20)
Continuity mistake: As Lance dances around with the purple smoke canister there's nothing in front of the helm of the boat under the radar dome. Later as the rocket attack that kills Clean starts a helmet appears there. (01:51:30)
Continuity mistake: As Chef and Clean sit on the back of the PBR reading their mail, we see Lieutenant Kilgore's surfboard wedged between the machine guns. It's there until the shot when we see Clean after he's been killed, where it disappears. (01:51:40)
Continuity mistake: Just as the rocket attack starts on the boat Chef is reading his mail and says, "hey Lance ". Look closely at the bullets on the machine gun right behind him, they're all draped to the left of the gun, no one has touched them but in a previous shot they were draped to the right the gun. The M-16 has also been moved. (01:51:40)
Continuity mistake: Just after the rocket attack that kills Clean starts there's a close-up of Lance manning the machine gun in the front of the boat. The Vietnamese spray this area with machine gun fire and chip away a lot of the green paint to his left under the radar dome. The next time we see this spot the paint is untouched. (01:52:00)
Continuity mistake: Several different boats are used in this movie as "PBR Street Gang" and they are almost duplicates of each other. In the scene where Clean is killed look at the handrail on the port side that extends from the rear of the roof towards the front of the boat. The last section is kinked up at a 45-degree angle where it's attached to the roof. Two minutes later we see a wide shot of a different PBR which has a gentle bend in this piece of metal rather than the abrupt bend on the other boat. (01:52:00 - 01:54:05)
Continuity mistake: There's a pole stored on the port side of the PBR. It's behind Chef after we see Clean's dead body. It's been removed in the next scene when they arrive at the French plantation. This pole has been used before in the movie and is stored in this spot and if it were somewhere else on the boat we would see it. (01:52:25 - 01:55:30)
Continuity mistake: After the rocket attack Chief Phillips looks back and says, "Chef, Chef check out Clean. Captain, he's hit". Look closely at the blood spatter on that the piece of metal that was behind him during the attack. Later as Lance takes over the helm of the boat there's less blood dripping on it. (01:52:30)
Answer: It's not any specific song; it's just the kind of generic piano music you'd hear at dinner at a high-class restaurant of the era. Think of scenes in movies, films, etc. set or made in the '50s and '60s, where the characters go to a nice dinner and there's someone at the piano playing unobtrusive music to accompany the food/conversation.