Other mistake: After the guys decide to rent the building, the shot of New York from the park is the very same one, though with different sky colour, to that of the moment when they are about to battle Gozer. Though it's a very wide and common shot of the park, the very same people are laying on the grass in the very same position in both shots (big screen recommended to spot it). (00:16:45 - 01:18:35)