Continuity mistake: At the end, the French soldier tries to kill Paul in the wet mud. When they finish struggling and spot the pistol on the floor, the mud on Paul's face is now dried and caked on.
Factual error: The parachute flare was not invented till 1922. This film takes place in 1918 but features one. (00:21:15)
Continuity mistake: Near the end we see a poster of a woman being pinned up in the German trench. This poster is folded and rolled at the bottom. At the end as the camera is panning out, the poster is flat and not folded.
Revealing mistake: The French tanks that attack Paul et al. Towards the end of the second act are supposed to be Saint Chamond tanks. There is only one of those left in the world, and it is not on screen: the undercarriage and tracks don't even come close to looking like that of a Saint Chamond, because it's actually a BMP-1 dressed up to look like a Saint Chamond.