At 32:10 the Drive-In theatre is shown with cars driving up to a screen. There are however, no speaker posts and apparently no speakers.
The artillery scenes used are stock footage which appear to be from various military areas. The footage includes one scene which appears to be mortar fire from Viet Nam at minute 53:27.
In that scene, is also shown more artillery smoke in the far distance, unrelated to the Giant Spider attack.
Beginning just minutes into the movie and continuing throughout the movie sporadically, the dialogue does not match the closed captioning.