you never been in a shooting stage, right............its a organized chaos, people shouting, mchine noise,and a real tigh schedule for shooting, sometimes the same studio is going to be used for another movie like in 3 4 months later...............so some mistake can go thourgh
although i admit that some could not happen...........for example in 007 world is not enough on the pier of the mafia russia fat guy, when 007 is on the middle of a gunfigth, he is handing a pistol, then it switch to the guys with a SUPRESED sub machine gun , with loud shots, and WORSE , when the camera comes back to 007 he is handing their sub machine guns, then bak to the guys, then back to 007 and he is back with his pistol.............i would fire the guy responsible for that.