Continuity mistake: In the first scene the librarian is pushing a cart of books. In one shot both her hands are gripping the back but in the next shot her left hand is holding the top shelf. (00:00:50)
Continuity mistake: The librarian is carting away books that are (for the greater length of the top shelf at least) leaning away from her. Cut, and they are positioned differently, about one third towards, a part in the middle away, and again towards her. (00:00:50)
Revealing mistake: In the very first indirect manifestation of the ghosts (the floating books), you can see on top of the stacks the rigs that allowed the strings to pull the books across [Noticed by Ivan Reitman during the DVD commentary]. (00:01:15)
Continuity mistake: The shot that introduces the existence of the Ghostbusters is a shot of the door of the "Paranormal Studies" laboratory inside Columbia university. It's a door that opens to the left and bears a glass panel with the names of the 3 scientists. When the shocked kid and Ray use it though, the door swings the opposite way. And when the Ghostbusters get back to their lab and find the Dean there, it's a double door with no glass, which was a prop built just for that opening shot. (00:02:45 - 00:13:10)
Continuity mistake: When Venkman is doing the tests trying to flirt with the blonde student, when she says that the figure on the card is a star, Venkman is first holding the card with his thumb and two fingers. But from the back angle, four fingers are seen extended. (00:03:20)
Continuity mistake: When Peter arrives at the library, the blue book he later slams is on the far left of the table. A frame later it's on the far right. (00:07:00)
Continuity mistake: The large blue book that Peter drops on the table to startle Egon disappears off the table in the next shot. (00:07:10)
Visible crew/equipment: In the library scene, when the ghostbusters are walking towards the old lady to ask her questions, if you look behind Ray's head to the right you can see a set light with a white tarp in front of it on the second floor of the library. (00:07:35)
Continuity mistake: Venkman is questioning the shocked librarian about possible use of drugs. Director Delacorte in the background is half turned towards them, but he's facing them directly in the close-up when Venkman says "Just asking." (00:08:05)
Continuity mistake: When Venkman walks down to the library's basement, his tie changes from skewed to straight. (00:08:35)
Continuity mistake: When Venkamn picks up slime from the library's drawer, the wood is first partially dry with chunks of slime, but a frame later appears all wet with no slime. (00:09:15)
Continuity mistake: Distance between the guys when they find the ghost librarian decreases significantly between shots. (00:10:40)
Continuity mistake: The future Ghostbusters don't have a clue yet what to do with the ghost of the librarian. They send Peter first, who tries to work his charm saying "Hello. I am Peter." Harold Ramis in the background is pointing the camera at a different height/angle between the two shots. (00:11:30)
Other mistake: After the trio stormed off the library, they are walking around the campus. As Venkman giggles mocking the "Get her" lack-of-a-plan, to the right of the screen there's an elderly lady who keeps staring curiously right at the camera. (00:12:20)
Continuity mistake: When the Ghostbusters run out of the library, an old woman in a blue coat is seen on the left side by the bottom of the steps. A second later she is all the way up and coming from the right side instead. (00:12:20)
Continuity mistake: The guys have just been thrown off campus. A liquored-up Peter walks Ray to the right explaining; "I believe that everything happens for a reason." Before the camera cuts away, you can see the head of a girl with a red ribbon in her hair that is going down the stairs. Next shot and she hasn't even set foot on the first step yet. (00:14:45)
Continuity mistake: When Ray first tries the fire pole at the station, he is holding it with his left arm with his right hand on the wrist. When he hits the floor, he is holding the pole with his right arm under his left arm. (00:16:10)
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)
Revealing mistake: A shot from above Dana Barret's apartment, from just above a statue looking down on the road below: The statue in the foreground is partially transparent. We can see the double yellow line on the street go straight through one of the statue's upper fangs, and one of the white lane dividers going through the statue's lower jaw. Viewed on Bluray disc. (00:16:50)
Continuity mistake: When we see Dana for the first time, there is an aerial shot of her taxi pulling over to drop her off. The front end of the taxi drives into the view of a tree, however when Dana gets out of the cab, the tree has vanished and there is a clear view. (00:16:50)
Answer: He places it on the altar just after they believe they have vaporized Gozer with the proton packs. At this point, thinking the ghost to have been destroyed, he sets it down as he believes the job is done and he will not need it.
Jazetopher