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.
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.
Continuity mistake: Paul and Kat are in a room. Paul is looking for items in his pockets whilst talking to Kat. The camera then switches to Kat and then quickly back to Paul. During this time, Paul's legs move from being straight out in front of him to having his knees bent; also, his hands have moved from being inside his pocket to resting on his lap. (01:01:13)
