Continuity mistake: When Joker is riding along in the chopper we can see its shadow falling on the ground below, only it's the shadow of a Bell Jetranger, not the Wessex/UH34 he is supposed to be in. (00:58:33)
Revealing mistake: The dead VC in the compound where Joker reunites with Cowboy is breathing. (01:09:00)
Continuity mistake: In the fire fight in the city near the end of the film, one of the men is firing a M-16 around a corner. As the camera angle changes he is seen firing left handed and right handed. Back and forth several times. Also in the same sequence the magazine in his gun keeps vanishing. One shot he has it and in the next there is no magazine in the gun and yet he hasn't moved. (01:14:32)
Revealing mistake: We find out at the end of the movie that the sniper is a young girl, but earlier when the first shot is taken at Eightball, you can see the sniper's fingers on the fore end of the rifle - they appear to be an adult male's fingers. (01:31:27)
Continuity mistake: When Animal Mother calls Cowboy to get the lone sniper, Cowboy chooses 4 guys to go with him: No-Doze, Stutten, Donlon and Rock. Then Joker and Rafterman say they wanna go too, so that makes 7 men (including Cowboy) but we only see 6. (01:34:00)
Factual error: In the sniper scene where Animal Mother disobeys Cowboy to go help 8-Ball and Doc, and Animal Mother peeks around the corner of a building to try and see the sniper and the sniper shoots at him, narrowly missing his face, the impact of the sniper's bullet on the wall and the sound of the gunshot occur a split second before the muzzle-flash in the distant window from where the sniper is shooting from. This would imply that both bullet and sound have travelled faster than light. (01:37:15)
Visible crew/equipment: When Cowboy, Joker, Rafterman and the other Marines are running across the buildings to get to Animal in the final sniper scene, watch the foreground. Right before they reach Animal, you can see they run by a crouching crew member, in the foreground at the bottom of the screen. (01:38:52)
Continuity mistake: In the part of the death of Cowboy, before he looks through the corner of the building to see the position of the sniper, there is a wall in good condition behind another wall which is broken. Later, when he goes back and starts to give orders, the wall that was in good condition is now broken without any reason for it to be and now the sniper can see Cowboy so she can shoot him. (01:39:20)
Continuity mistake: During the first firefight scene a soldier fires a M79 grenade launcher and hits one of the second-floor window. The glazing of the second window in the same floor is also destroyed. In the next shot the glazings of both windows are intact.
Factual error: When 8-ball gets shot, in the shot which shows the platoon ducking near a wall with Cowboy, Joker and Animal Mother in the front, there are two weapon related errors. Cowboy's M-16 has a nickel (silver colored) firing assembly and Joker's M-16 has an A2 type pistol grip. The A2 types were introduced somewhere around the 80s, and nickel plated assemblies are rarely used (and were invented after Vietnam, too). The nickel assembly is visible at the beginning of the shot, and you can see the A2 grip when Joker is changing magazines (while Cowboy shouts cease fire).
Continuity mistake: In the scene where the sniper is shot, You can see blood on her face (especially on her upper lip) when she falls down after being hit, but when she lies on the floor afterwards, there is no blood on her face anymore.
Continuity mistake: During the graduation parade, if you look at the background you can see many large squad bay buildings with a few single trees in front of them, this scene seems to be shot at the actual Paris island. However when they show a close up of Joker's platoon in parade, the background changes to mostly trees, with only two or three small buildings behind them.
Continuity mistake: In the bathroom scene on the last night of boot camp, Pvt. Pyle is 'training' with a rifle. As he snaps to attention, the shot from behind shows him with legs slightly apart, a second later the shot from the front shows him with his legs perfectly together, yet he never moves.
Continuity mistake: When the tanks are moving into the city with the Marines i.e. after meeting Private Cowboy, Animal Mother and the rest, they run into a firefight. When they stop shooting and are reloading watch the leader's ammo clip. It's missing in one shot of him, in the next he's ejecting the magazine and putting in a fresh one before shooting the two Vietnamese with it.
Continuity mistake: After Cowboy is hit by the sniper Animal Mother fires wildly and destroys part of the "My Toan" sign. A few seconds later you can see it is intact.
Continuity mistake: When Joker and Rafterman are in transit on the chopper, we see the gunner firing out the cargo door. We can see out the cargo door that the ground is pretty far away, the chopper is obviously pretty high up in the air, so high that if there were people down on the ground it would be rather hard to see them. However the camera switches to the gunner's point of view shooting at people, and the chopper only seems to be about 20 feet off the ground.
Continuity mistake: When Hartman punches private Joker you can see Hartman swing with his left hand in one shot and a split second later (angle from the floor) when Joker has been struck, Hartman's right hand has made contact and is pulling back.
Continuity mistake: After Lt. Touchdown has been shot, behind the tank, he falls to the ground with his rifle still grasped in one of his hands but when the marines move in to aid him his rifle has vanished.
Revealing mistake: When Private Pyle shoots himself you can see that the blood splatters from the side of the screen instead of going straight back from the back of his head.
Factual error: Joker would not have been allowed to go through basic training and out into the field with wire-rimmed glasses. He would have been issued plastic/cellulose-framed Regulation Prescription Glasses (AKA BCGs or "Birth Control Glasses") like Private Cowboy's.
Answer: It was Gustav Hasford's idea. It happened in the original book that the story is based on, "The Short Timers."
Captain Defenestrator