To compare, review the scenes where Dana Barrett enters her apartment with the groceries to find the demon in her refrigerator and then review the scene where Dr. Venkman investigates the kitchen. Even though Dana supposedly left the apartment after finding the demon in her fridge you will notice as Dr. Venkman investigates that several things have shifted. The bag of Stay-Puft marshmallows has been propped up at a different angle so that the bag is now completely facing forwards and her brown grocery bag, which looked almost perfectly unfolded when she set it on the counter has returned to its strained and slightly crumpled look (this is the way it should've been since she was cradling it and then set it on her coffee table but it is not the way she left it). You will also notice that in the apartment there was a fruit basket on the back countertop which has disappeared by the time Venkman arrives, the eggs are also shifted in their package and a bit more cleaned up where egg white once hung over the edge of the carton. I'm also not sure that the step ladder that appears by the back corner cabinets was there when Dana first enters the apartment. Judging by its placement in the investigation scene it still should have been visible behind Dana's grocery bag when she comes in and it is not. These inconsistencies seem trivial but a) are funny to notice and b) make it a little suspicious to believe she didn't return to the apartment.