Continuity mistake: In the beginning after the teacher is shot the Russian shoots into the classroom. During the first view you see all of the students ducking and right before they cut to the next shot there isn't a dead kid on the window but when they come back to that shot there is.
Continuity mistake: When the small band of troops comes up the mountain to take pictures and read the sign, one of them snaps a photo of the view. We see a static shot of what he is looking at, trees covered in snow and fog in the valley. Later however, we see the same view. There is no snow on the trees and no fog down below.