Revealing mistake: At the end of the film, the screw is tapping on the window to get out and Hogarth moves to put the box down. The box completely vanishes from the shot for a few frames towards the end of the shot.
Continuity mistake: When Hogarth knocks his face into the tree after running, he has a lot of blood on his face, but in the very next shot, in which he turns around after hearing the giant, the blood is gone.
Continuity mistake: The amount of Hogarth Hughes' name that appears on the crushed BB gun shifts a bit from when Mansley picks it up and when it's shown later in the film. In the first shot, all that is seen is Hog Hug. Yet later, small bits of the second H in Hughes are visible with the name having been shifted to the side a little, as well as shifted down a little, as the wood grain line cuts through the bottom of the U at first but now is at the top of the U.
Answer: It was a laxative to make him go to the bathroom.