When McB is playing cards the deck has both the pictures (hearts, spades, etc) and the number in the corner. They didn't put #s on cards until 1864 and it was extremely rare to see a deck with them until 20-30 years after the war
In the opening scene (c. 3 minutes) the little girl doesn't actually pick the mushrooms, she just gathers up previously picked (and very clean) fungi by their cups. To pick a mushroom in the wild one must grasp it at the bottom of the stem or use a knife. Picking a mushroom by grasping the cup would break it in two.
When Carol leaves the house to find McB, she posts him in the gazebo playing cards. He is laying out the cards with his right hand, but when the camera angle changes to show Carol arrive, he is laying out the cards with his left hand.
As Carol leaves the gazebo after Edwina arrives, she has to run a good distance to get to the tree where the blue rag is kept to alert patrols to "yanks", but when McB hears horses, he can see the front gate from the gazebo.