The hotel this movie takes place in is supposed to be the Rochester Hotel, but during one of the final scenes the hotel's awning is visible and "The Biltmore Hotel" is written on it.
Visible battery hatch on the belly of the "petrified" dog.
When one of the East Point Military boys lights a small blow torch you can hear a strong blow torch sound, but for a moment there is simply a weak flame similar to what a match would produce.
When the boys from the East Point Military Academy shoot a grappling hook into the window, you can see the guide wire it travels on. You can also see the hole that was precut into the painting that the guide wire passes through.