Factual error: Prior to WW1, Colonel Ludlow picks up Samuel and Susannah at the train station in an all steel Model T Ford. This style of car did not come out until 1917. The correct car would have brass lights and radiator.
Continuity mistake: When Alfred confronts Tristan on the porch, the morning after Tristan has done the deed with Susannah, the buttoning of Alfred's shirt becomes reversed, then changes back again.
Plot hole: During the war sequence, when Samuel dies, how necessary was it for the two Germans to go through the trouble of setting up a machine gun to shoot him? I find it hard to believe they had no other weapon but that. It seems to have been done only to build suspense.
Continuity mistake: When Samuel dies in the movie, if you watch closely there is blood running down his face in only every other shot.
Continuity mistake: When Suzanna comes in for dinner the first night there, all the guys raise something to give her, but Tristan goes to raise his plate. But cutting back from her reaction, he has only lifted his glass to drink. (00:15:20)
Continuity mistake: Susannah's hair problems during her first encounter with Tristan after his many years of absence have been stressed already. But Tristan's hair has an even stronger mind of its own, as there is a wide strand combed back covering his parting, which looks as if it has been fixed elaborately, but which nevertheless comes and goes during the scene. (01:25:50)
Continuity mistake: After Tristan's second return he comes to Susannah's house. They make eye contact while he is still standing behind the wall. The camera cuts to Susannah and then back to him, and he is standing in the garden, with no time in between to walk further down to the gate and enter. (01:24:55)
Visible crew/equipment: When the British troops try to overrun the German lines soldiers are catapulted into the air by German grenades. At least once you get a good view of something like a springboard that was used for this purpose, that is when you hear Samuel's voice saying :"...the souls of those wounded so terribly...". (00:33:50)
Factual error: It has already been mentioned that, although the war scenes are set in early 1915, gas was not used until April of that year. There are further inaccuracies regarding this particular scene. The mask worn by the German cavalryman is not the sort of mask that was in use in 1915. It looks like a late WW1 or WW2 gas mask. Furthermore, since horses can also suffer from gas, a cavalry horse taking part in an attack in which gas was used would also be equipped with a gas mask. However, by early 1915, when both sides were dug into trenches, cavalry would not have been used anyway.
Continuity mistake: During Samuel's death where Tristan is cradling him in his arms, there is a stream of blood at the corner of Samuel's mouth. The camera cuts to Tristan's reaction, but when it cuts back to Samuel, the blood is gone. In later shots of Tristan preparing to remove his heart, the blood stream reappears. (00:44:00 - 00:44:55)
Continuity mistake: When Tristan returns to see Suzanne at her new home with Alfred, her hair is down. But in every shot her hair is either pulled behind her ear, then both sides in her face, then one side pulled back, and so on. (01:25:55)
Visible crew/equipment: In the opening scene, when the COL is sitting in front of the cabin, a modern pickup or van can be seen in the background.