The United Artists logo seen in the opening credits of the film was from the company's archives. All the films released under United Artists at the time of Undertow's release had a different logo. As a child, director Green always saw that logo and was unsettled by it, and for that reason, he used it in the film.
David Gordon Green originally wanted to title the film "The Narrow Pilgrim," focusing on Tim in his pilgrim costume at Thanksgiving. The original story was going to put Tim more in the focus, along with his eating disorder. He is thin and ratty, due to his pica condition, and in a pilgrim costume: "The Narrow Pilgrim." However, he quickly began to change it due it him discovering that it would not be a very marketable title.
Chris and Tim start down the staircase to escape the house,
Tim has a backpack slung over his left shoulder. The backpack is gone when they reach the bottom of the steps. Later, when they run up to their room, Chris packs some items in the backpack that is lying on the bed.
When the black woman they take refuge with is in the bedroom, she finds the contact details of the boys written on the inside flap of the backpack. Later when the boys run away because they find out their uncle is coming, they just run straight from where they were outside, with no detours to pick up the backpack. However, later, Tim is shown with the backpack.