Continuity mistake: After Captain Willard looks at the picture of Colonel Kurtz being decorated by General Westmorland, they're all startled by the "Arc light" B-52 strike, note the rear machine gun is pointing forward and a helmet is hanging from the middle machine gun. In the next shot the rear machine gun is pointing aft and the helmet is now gone. (00:24:05)
Continuity mistake: The actual napalm attack burns quite a large area of the tree line and just two shots later Colonel Kilgore speaks the famous lines, "I love the smell of napalm in the morning!" At this time, when we see this area is still smoking, quite heavily, however, the amount of destruction is much less and there is very little fire visible. (00:48:55)
Continuity mistake: On the dock Chef listens intently to the Frenchmen who is yelling at them. A smoke canister is lit up on the back of the boat but in the next shot there's a close-up of Chief Phillips with no smoke behind him. (01:57:25)
Continuity mistake: As they prepare to lower Clean's body into his grave Lance stands to his right and reaches down to lift the flag. According to his wrist watch it's 11:45 but twenty seconds later there's a close-up of Chief Phillips' watch and it's now 4:10. (02:01:10)
Continuity mistake: When they approached the French plantation both doors of the demolished building are open. Later as Captain Willard walks through them, the door on the right is closed. (01:55:35)
Continuity mistake: In one shot we see the helicopters firing on the huts along the Vin Din Dop beach and the four missiles go directly into the beach nowhere near the huts. In the next shot the middle hut blows up. (00:40:00)
Continuity mistake: As Dennis Hopper leads Captain Willard up the steps we see the wall with "Apocalypse Now" written in white. In the previous shot there were a lot of sand bags there, now there is just a big boulder. (02:31:35)
Continuity mistake: When Francis Ford Coppola appears in the movie as a TV director, he asks the captain to, "Just keep on going," and a small boy is playing on a black Agent Orange drum in the background. If you watch the labeling on the drum you can see that it's been moved between shots. (00:25:50)
Continuity mistake: The day after the USO show at Hau Phat, the boat leaves and there are five men working on the stage. In the next shot there are three. (01:11:35)
Continuity mistake: Captain Willard says, "Whatever was going to happen, it wasn't gonna be the way they called it back in Nha Trang". Note the light pole in the center of the boat, the second blue light from the top is shot out however there hasn't been any battles since the French plantation scene when all four blue lights were intact. (02:21:25)
Continuity mistake: In a close-up of a soldier on a helicopter gunship shooting down at the people of Vin Din Dop below we can see the bridge in the background and it's already been blown up. This doesn't actually happen till later in the scene. (00:40:05)
Continuity mistake: In the boat Captain Willard reads more about Colonel Kurtz' and fingers through his three Green Beret applications. Right after the captain says, "But when he threatened to resign, they gave it to him," he stops on a prop sheet that had the real names and dates erased and new names and dates typed in using a different typewriter that has darker numbers and letters. (00:01:25 - 01:01:25)
Continuity mistake: In the scene where they stop the junker boat that they think might be smuggling supplies, as you watch the many scene angles, you can tell that the sun is at different points at different times. Where Willard is sitting at the side of the boat the sun is nearly set, and at one point is below the horizon. At another time, you can tell, the sun is several degrees above that, and in one angle, it is practically noon. Also, the boats change angles, toward the shoreline, possibly to shoot a scene from a better light angle. (01:34:08)
Continuity mistake: The vehicle on the bridge that is attacked by the helicopter has three men in it. In the first shot of it exploding one man falls to the right and two men fall to the left. In the next shot as it falls off the bridge all three men fall to the left of the vehicle. (00:41:45)
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: During the arrow attack as Captain Willard grabs Chief Phillips to try and make him stop shooting, the sun can be seen setting over his shoulder. Several other shots in this scene, like the next one, were filmed in the mid afternoon with the sun overhead. (02:22:20)
Continuity mistake: Captain Willard is wearing green, tan and black camouflage trousers on the PBR when they spot Kilgore's air-cav unit. They immediately proceed toward shore and as he jumps off of the boat he's wearing different camouflage trousers, which are brown and green. (00:24:15 - 00:25:15)
Continuity mistake: As Colonel Kilgore gets into his helicopter the trumpet player is standing right there next to it blowing charge. In the next shot as the helicopter takes off he's not there. (00:34:50)
Continuity mistake: The attack on Vin Din Dop starts out as a bright sunshiny morning and stays that way until Clean and Chief Phillips watch their boat drop into the river. There's no cut in the action but after this shot the cloud cover turns darker and it's late afternoon. (00:47:35)
Continuity mistake: The gentleman in the tan jacket sitting next to Roxanne says, "Look an egg" and the glass in front of him fills up between shots. (02:07:20)
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.