Visible crew/equipment: As they pull away from the Do Lung Bridge, look closely and you can see water spraying up and turbulence from the propellers of the camera boat in front of them. (01:48:40)
Visible crew/equipment: After Clean is killed in the rocket attack there are several shots where the camera crew films the front of the PBR as it approaches them. The spray and turbulence from their boat in front of the PBR can be seen in all of these shots. (01:52:20)
Visible crew/equipment: After Clean is killed there's a shot of Lance sitting on the back of the boat holding a mirror in his right hand. This is not the actor Sam Bottoms but a longer haired thinner stand-in who's not wearing the black wristwatch that Sam wears in every other scene in the movie. (01:54:10)
Visible crew/equipment: After the man sitting to the right of Roxanne gets up and leaves there's a wide shot of the table with Captain Willard at the right. If you look closely at his hair you'll see the shadows of crew members moving between him and the stage lighting throughout this shot. (02:11:15)
Visible crew/equipment: After Chief Phillips is speared if you look closely at his left shoulder you can see his shirt bunched up by the harness underneath that holds both ends of the spear to his body. Later you can see a blood bag underneath his tee shirt as he lies on the floor of the boat dying. (02:22:40)
Visible crew/equipment: After he tells him what his mission is Chef says to Captain Willard, "That's f***ing typical, shit, f***ing Vietnam mission". Look at the shoreline about 30 feet past the boat as a crewmember ignites a purple smoke canister. (02:24:20)
Visible crew/equipment: As he gives the captain some water, Dennis Hopper says, "Why would a nice guy like you want to kill a genius?" Look closely at the ladle and you can see the reflections of two crewmember's heads moving in front of the main stage light, one on the left and one on the right. (02:43:00)
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.