James and his contractor prepare a batch of ANFO (ammonium nitrate + fuel oil) to blow up the mound. This is a 'tertiary' explosive, which means you cannot set it off with fire. It would just burn. To set off the detonation, you need to explode a secondary explosive, like a stick of dynamite, which in turn needs to be set off with a primary explosive, like a blasting cap.
When James is driving back from the old man's house, he tries to call home but gets no answer. The sound effect you hear is one of a phone off hook, not a busy signal.
Any responsible teacher would not give kids ant farms with a queen, since queens can live for years, producing ants for 1-20 years. Ant farms are not designed to house a queen ant and the thousand of young she produces.
Whenever Louisa comes back from the mound, her feet and lover legs are covered with wet mud, but there is no wet mud inside or around the mound. And there are no holes in the mound for her to get inside. It is all undisturbed grass.
After John James crawls into the small burial mound, he stands up and walks quite a distance through large passageways. They are on the same level, not dug out below the mound. And they have floors! They have lots of tree roots hanging down, although there were no trees on the mound.
Shooting a double barrel shot gun three time without reloading, and he only had two shells to start with.