Paavo Hakala is wounded on December 18 and gets a week's leave. However, he is back to the front already on December 23.
Near the end of the movie, Private Pentti Saari shoots a captured Semi-Automatic Rifle SVT-40, but he reloads after each shot (it is possibly caused by shooting blanks, which have not enough power to reload the rifle). The SVT-40 itself was introduced after the war, and it should be older, slightly different model SVT-38.
Whenever a Soviet Polikarpov I-16 fighter strafes the Finnish positions, it uses it's wing cannons, yet there are no explosions. Polikarpov I-16 fighters have 2.0cm ShVAK cannons in their wings which fire explosive ammunition, so there should be explosions.
Several attackers and defenders survive nearby explosions that would in reality perforate them with shrapnel and other debris.
During the battle of Äyräpää, some attacking Russian soldiers can be seen wielding modern assault rifles.
When the men chase after horses, one can briefly see an electric cable pole. It has a grounding wire with modern black-yellow coating.