When Salem is returning to his cell, the second time, just before he locks the door.
When the Inspector and Doctor are existing Salem's cell.
The police never see the many footprints Salem left in the snow.
When Salem is swinging on the rope and climbing down the tree, it's an obvious double with a stockier build and darker hair.
When Salem makes his second escape, at night after lights out, all scenes outdoors until he returns to his cell and pretends to sleep are obviously daylight. No attempt has been made to use a day-for-night filter.