Just before Sefton reveals the spy, he throws an open jackknife onto the table and says, "Here's the knife to do it with. Only make sure you got the right throat." The knife quivers and barely sticks in the table. Shortly after, the knife is stuck firmly in the table, more upright.
Stanislas "Animal" Kasava is falling on his butt into the mud, but his white underwear isn't getting dirty. Two minutes later running to see the Russians girls, he falls again and then he's muddy all over.
When Cookie starts to remove the radio from the pants leg of the soldier on crutches, it's visible right at the hem, but when the camera cuts away and then cuts back a moment later, Cookie is reaching farther up the pants leg to remove the radio.
At the movie's beginning, it says that at least the two escapees will have the longest night of the year (December 21st). Towards the end of the movie, it's Christmas eve (December 24). Yet at least two weeks of events have elapsed since the movie's beginning and the end.
When William Holden's character is laying on his bed on his back and first notices the swinging light bulb's shadow near his feet, the next scene shows the light from his bunk and there is no light source behind the swinging light that could have cast that shadow.
It's December 1944. Every morning at 6:00 it's roll call for the prisoners of Stalag 17. Although in the middle of December in southern Germany the sun will never rise before 8:00 the roll call in the movie is in full daylight.
Schulz is identified as a Feldwebel or Sergeant but he is wearing the rank insignia of an 'Unteroffizier' or Corporal. The German Army's rank insignia were on the shoulder straps. A Feldwebel's insignia would be 'lace' that went around all edges of the shoulder strap plus a star or 'pip' on the strap. Schulz's shoulder straps do not have lace at the bottom of the strap nor do they have have stars; that is the insignia of an Unteroffizier.
When Sefton is explaining how he got hold of the telescope, he explains that he got together a "few lenses and a mirror". The telescope he has in the barracks is a refractor telescope, which doesn't use mirrors.
In at least two scenes, German solders are seen using US Browning 30 cal. machine guns; some still think of it as an error, but the use of captured enemy equipment was common by all sides in the war. A POW compound would be the ideal place to locate captured weapons, with a relatively limited ammo supply, while they still served to deter escape.
The map of Germany in von Scherbach's office in 1944 would include not only Austria and Sudetenland but also Gdansk/Danzig and the Polish Corridor, large parts of western Poland and the Saarland, all considered ethnically German by the Nazis and incorporated into the Reich. This could simply be an obsolete map never discarded.
We learn from the escape plan in the beginning of the movie that the Stalag 17 prison camp is located on the river Danube near Linz, which is on the Austrian and German Border. Later in the movie, when the prisoners are watching the women in the Russian compound, Cookie claims that on a clear day, you could see the Swiss Alps with this telescope. Nobody could see the Swiss Alps with even the best telescope, from this point of view, because the Austrian Alps would definitely be in the way. This could be a simple exaggeration of the power of the telescope within the character of the prisoners whose scientific knowledge is limited. With a good telescope one can see mountains on the moon; no telescope can ever show anything beyond the horizon.