Trivia: Two points in the movie where you can see Staypuft Marshmallows: the first is next to the eggs on Dana's worktop when the eggs start to cook, and the second is when the beam of light is coming out of the Ghostbuster's house, there is a wide shot of it and on the left of the screen there is a billboard advertising Staypuft Marshmallows.
Trivia: The "marshmallow" at the end of the movie is shaving cream.
Trivia: After the librarian signs out in the downstairs section of the New York Public Library, she passes the card catalogue shelves which open behind her and suddenly hurl their contents into the air. To achieve this effect, technicians were standing behind the shelves to push them out and then used a copper pipe to blow out the contents.
Trivia: The party scene at Louis Tully's apartment was entirely improvised.
Trivia: Harold Ramis states in the DVD commentary that the "experiment" that Venkman conducts at the beginning of the film is inspired in part by the Milgram Experiment. In the Milgram Experiment, people were told that they would be giving a person increasingly powerful electric shock whenever the person incorrectly answered a question from a list that was read off. (The reality was that the person being "shocked" was an actor and that the generator was fake; the experiment was a test of whether the subject would give a person lethal shocks just because an experimenter was telling them to do so.)
Trivia: The first time the heroes use their proton weapons (in the hotel sequence), you can see (using slow-motion) that the rays don't actually come from the weapon, but from their target. The rays were "drawn" during post-production and, apparently, it's easier to start drawing from the target to the weapon. (00:31:46)
Trivia: The opening couple of shots were actually shot at New York Public Library. The crew could only film until 10am for one day. All of the scenes in the backroom of the library were filmed at the Los Angeles Public Library.