Near the beginning of the film, there is a montage showing, among other things, a resistance fighter tied to a post and being executed. A square white piece of paper is attached to his torso as a target. Immediately after he is shot we see four bullet holes in the paper forming a "parallelogram" pattern. Moments letter, in a close up of the dead fighter, the bullet hole pattern is reversed. It's pretty obvious that the paper had been taken off between scenes and then reattached backwards relative to the first shot.
When the storekeeper fills the box with groceries, an overhead shot shows him adding plenty of apples. In the next close-up shot when he adds chocolate bars, there are fewer apples, and a big white-green box that wasn't present before.
Citron picks up a British Sten SMG in the basement scene and fires it. A few seconds later he has a wooden stocked sub machine gun instead (the Sten had a steel framed stock) which looks like a Finnish Suomi SMG.
When Hoffman's drivers are held down at gunpoint in the rain, you can see that the street is dry several yards behind the action and sunshine in on the background buildings. Obvious use of overhead sprinklers.
The goof item below may give away important plot points.
Near the end, The Lemon manages to kill several of the soldiers on the lawn. Not long after, he proceeds to walk out of the house he was barricaded in... with no visible signs of any of the soldiers he killed.