Continuity mistake: A little old Vietnamese woman wearing a bright red scarf around her neck is feeding bullets into the machine gun. Six seconds later as the machine gun is blown up her stunt double is not wearing the bright red scarf. (00:40:55)
Continuity mistake: In an aerial shot a helicopter pilot says, "I got a vehicle on the bridge " but if you look closely there's no vehicle on the bridge until the next shot. (00:41:40)
Continuity mistake: A vehicle on the Vin Din Dop bridge is shot by a rocket from Kilgore's helicopter and Lance says' "nice shot Bill" after he sees the car blow up. Colonel Kilgore's helicopter has surfboards on its sides not rocket launchers as was seen when they took off in the last scene. (00:41:45)
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: After the 'Valkyrie' helicopter attack, there's a close shot of a soldier who shouts: 'I'm not going.' Another soldier turns back to the chopper to pull him out. Then there is a long shot of the troops at the choppers and you see the same soldier turning back to the helicopter. (00:42:15)
Continuity mistake: As the helicopters land in Vin Drin Dop "The Ride of the Valkyries" is still playing but none of the helicopters have speakers hanging out of their side doors to play the music the way they did before. (00:42:30)
Continuity mistake: After the helicopters land on the beach at Vin Drin Dop a soldier yells, "I'm not going, I'm not going" and we see huts that were blown up and burned down earlier in the scene untouched and as good as new. (00:42:50)
Continuity mistake: Just before the Medevac helicopter lands in the Vin Drin Dop plaza, a soldier machine guns 13 urns sitting next to the building on the left of the courtyard and the building also explodes. In the next shot of the medics working on the injured soldier the 13 urns are back and the building hasn't exploded yet. (00:43:05)
Continuity mistake: As the chopper pilot circles the courtyard he says, "We've got wounded down there" and a yellow flair is in the center of the courtyard. In the next shot of the soldiers running around down below we see the center of the courtyard but the yellow flare is not there having been replaced by a Vietnamese hat. (00:43:10)
Continuity mistake: In the first close-up shot of the soldier wounded in the Vin Din Dop courtyard there are two medics working on him. In the next shot there is a third kneeling by his left leg in the exact spot where the cameraman just stood in the previous shot. (00:43:20)
Continuity mistake: In the first close-up shot of the soldier wounded in the courtyard the medic behind him tries to give him some water as the camera pans away to two Vietnamese civilians for a second. In the next shot the medic is still holding the canteen but the injured soldier now has something hanging out of his mouth, that looks like a piece of string, which wasn't there in the previous shot. (00:43:25)
Continuity mistake: When the Medevac helicopter first lands in the Vin Din Dop courtyard there are only soldiers on the left side of it putting the injured man in. In the next shot five soldiers and a Vietnamese woman appear standing on the right of the helicopter who weren't there before. (00:44:05)
Continuity mistake: Before the Medevac helicopter explodes in the Vin Din Dop courtyard its main rotor is rotating at full speed. In the next shot as it explodes the main rotor is barely turning. (00:44:10)
Continuity mistake: Right after the helicopter pilot says, "my tail rotors out, I've got control" they blow up the entire Vin Din Dop bridge ending with the side closest to the beach. In the next shot they blow up the same side of the bridge again closest to the beach. (00:44:45)
Continuity mistake: When Colonel Kilgore shows Lance the surf as they fly over the beach he says, "look, good six-foot swells" and his surf board is not on the side of his helicopter as it is in the next shot when they land. (00:45:10)
Continuity mistake: On the beach Colonel Kilgore says to one of his soldiers, "what do you know about surfing major, you're from New Jersey" look closely at the Vietnamese prisoners walking on the opposite side of the beach. They're always walking from left to right but several times in this scene they change their starting position from further down the beach (left of screen). (00:45:50)
Continuity mistake: There have been many shots of the surfboards as they flew to Vin Din Dop and they were all on the skids of the helicopters, now when Colonel Kilgore says, "do you wanna surf, soldier" we see the surfboards placed next to each lengthwise through the helicopter with their fins sticking out the side doors. (00:46:05)
Continuity mistake: After the helicopter attack when the chopper drops the patrol boat into the water, you can see the canopy and the radar type antenna break and collapse. When you see it again it's in perfect condition. (00:46:55)
Continuity mistake: As Colonel Kilgore calls out to the soldiers surfing in the water Captain Willard's band-aid on his right cheek appears out of nowhere for the first time in the movie. He had no band-aid on his face before this and we don't see him put one on, and there's no indication from the last time we saw his face that his scar started to bleed. (00:47:00)
Continuity mistake: Before the napalm attack we see a shot of the spotter plane flying over Vin Drin Dop and the place hasn't been attacked yet even though the battle has been going on for a while. There's no smoke and the bridge is still intact. (00:47:25)
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.