Continuity mistake: Clean's burial is two minutes of uninterrupted action. When they first carry him over he's on a bamboo stretcher. One of the soldiers proceeds to take the flag off of him then another puts it back on. When we see his body again a few seconds later the flag is in exactly the same spot but the stretcher underneath is gone. (02:00:45)
Continuity mistake: As Hubert stands at the window he says, "The generals and the colonels believe it's impossible for the Viets to get the cannons up there in the mountains". It's clear to see that all the windows are closed but the next time we see them the second one from the bottom is open even though no one has gone near them. (02:08:55)
Continuity mistake: When Captain Willard flies in by helicopter to meet up with the PBR at the Texaco fuel depot, we see only one PBR with a flag waving in the front and a radar dome on the back of the roof. This is not the same boat that we see in the next shot in which the flag and radar dome are reversed. (00:19:25)
Continuity mistake: Captain Willard and the men get off the PBR and walk to their right about 30 feet in the direction of the hut that is destroyed by the boat with the teeth painted on it. In the next shot when they run into Francis Ford Copola they're back to where they started as we see the boat directly behind them. (00:25:50)
Continuity mistake: When the Playboy helicopter lands the band members on the right stage are crouching behind their equipment, but in the next long shot of Bill Graham speaking to the audience they're standing there ready to play. (01:06:35)
Continuity mistake: Dennis Hopper and Chef are looking at the heads on the ground, Chef turns to face him as Hopper says, "You were gonna call him crazy?" In the next cut Chef is looking forward at the heads again. (02:33:40)
Continuity mistake: As Chef and Captain Willard continue walking through the jungle looking for mangos Chef says, "Hell, I joined the Navy" and he's holding his gun out in front of him with both hands. In the next shot he's carrying it over his right shoulder. (00:57:00)
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: Clean's dog tag and cross change between scenes. When he first hears the "Arc light" B-52 strike we see the cross hanging at the same level as the dog tag then when he meets Colonel Kilgore the chains have been rearranged so that the dog tag is two inches lower than the top of the cross. (00:24:10 - 00:30:05)
Continuity mistake: Before the napalm attack as Colonel Kilgore gives Lance a pair of shorts to wear while he's surfing, there is yellow smoke visible on the beach between them and the other side of the bay. As the jets fly by and this spot is again visible the yellow smoke canister is not there. (00:48:35)
Continuity mistake: They took the flag from the PBR (which is removed from the roof of the boat the next time we see it) to cover Clean's body at burial. It's not the same flag, the last red stripe on the bottom of the PBR's flag is torn off as we see at the French Plantation dock. The flag on Clean's body has the last red stripe and also has a shorter white stripe on it's bottom. There's no indication that there is more than one flag on the PBR (redux version). (02:00:05)
Continuity mistake: The red wind spinner in front of the helm of the PBR appears for the first time after the attack that killed Clean than disappears in the French Plantation scene (redux version). (01:54:00 - 01:57:40)
Continuity mistake: As Clean tries to get some fuel the sergeant says, "Eight bucks for that camera" and Captain Willard grabs him by the throat and pulls him over the desk. At first the Captain has a cigarette in his mouth than in the next shot he doesn't. (01:05:00)
Continuity mistake: When Captain Willard runs into the photographer when he reaches Kutz's compound the scene keeps jumping back and fourth between the two characters as they walk around. The photographer is wearing a red headband. As the film shots keep jumping back and fourth between the two characters the headband changes from being folded flat to being rolled up across his brow.
Continuity mistake: Just as Captain Willard grabs the sergeant by the throat and pulls him over the desk Lance reaches his left hand up to his face, then in the next shot his hand is at his side. (01:05:25)
Continuity mistake: Discussing the map with Captain Willard Colonel Kilgore says, "Mike, you know anything about this point at Vin Drin Dop? " and Mike goes from looking at Lance on his right to looking at the soldier on his left between shots during the beach party. (00:32:50)
Continuity mistake: Captain Willard walks up to a soldier and asks him, "Where can I find the CO". At first he has his right hand on the soldier's left arm then in the next shot he's not touching him at all. (00:26:20)
Continuity mistake: In the second shot of dinner at the plantation a French boy is speaking to the people seated at the table. There's no centerpiece or flowers in the middle of the table but there is in the next shot. (02:02:50)
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: They dock the boat on the side of the river and as Lieutenant Kilgore flies over looking for his surfboard we see a long rope running from the front of the boat to a tree. It's in some shots but not in others. (00:53:45)
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.