Other mistake: When the Major shoots the rope out from under the slow soldier, the rounds should have gone through the floor but did not. There aren't even marks on the floor.
Other mistake: There is a lot of shooting with automatic weapons, and a lot of Germans fall - but there is a remarkable lack of bullet holes anywhere; even in such tight quarters as the bell tower, where bullet holes should have appeared.
Other mistake: After Reisman beats up Franko at the beginning, Reisman asks the guard to have 2 prisoners take him back to his cell. After that, Reisman says "lets see if they can do some close order drill now." During the drill, there are 11 prisoners marching instead of 9 as 2 of them took Franko to his cell.
Other mistake: Just as the attack begins on the chateau a German officer is shown for a second time shouting for everyone to head to the cellar. Immediately after this, a younger officer is shown motioning toward his holster, as though he intends to draw his gun but there is no gun in it.
Answer: Rifle firing pins?