While fighting a large German with a tattoo on his chest, Martin kicks the German in the chest and a part of the tattoo goes missing. Next cut it's there again.
When Boon enters the pavilion after Martin kills Steiner, he is carrying a MAT-49 French sub-machine gun. After Boon slams Martin through the table during their fight, Martin grabs the gun off of the couch, but it is now an MP-40.
At 3:57 the assailant goes into the water with tattoo across chest. Upon emerging from water assailant is missing most of tattoo at 4:02. Then at 4:07 assailant has tattoo back.
At 1:17:55 People are putting white paint on Martin's face. For the next several seconds, camera angles change back and forth, and the amount of white paint on Martin's face keeps changing.
While firing the belt fed MG42 machine gun, the camera zooms in to show that the cartridges are clearly blanks as they don't have a bullet tip but instead a pressed opening.
In the scene where Martin is first helping out as a bar back there is a table being cleared of beer bottles. One of these bottles is clearly a Lagunitas, a CA brewing company that was founded in 1993.