Revealing mistake: Tully just ran away from the apartment building screaming. The doorman repeats to an incoming couple "A bear, in his apartment..." The husband pulls his wife back without for a single moment glancing at the direction the beast (or its growl) come from; he stares constantly at the foreground. (00:54:00)
Continuity mistake: Dealing with Tully, Annie Potts says one rather oddly foreshadowing line to Harold Ramis about his death, and then clings to him. Ramis puts a hand on her shoulder, and the position is different in the next shot. (01:02:00)
Continuity mistake: When Venkman is in Dana's bedroom the quantity and quality of light coming through the window changes between shots; look at the side of the window when he is counting down, for instance. (00:58:30)
Continuity mistake: During the scene with the possessed Dana in bed with Peter, the pillows rest at different heights against the bed's headboard. (00:57:30 - 00:58:40)
Continuity mistake: When Dana struggles with the literal arm-chair, one of the arms pops out of the top of the right armrest and a clawed hand clutches Sigourney Weaver's face. Change of camera angle, and not only she is struggling against the demonic limb in a different position, but the hole is gone from the top of the armrest, the arm is sticking from the side. (00:51:45)
Continuity mistake: The lighting in the scene with Venkman stalking Dana outside the concert hall is inconsistent. For instance, when he quips "I've got hundreds of people dying to abuse me", Dana's stiff friend leans against a fountain that is bathed in sunlight. Mere moments later the section of the square is in the shade. (00:43:10)
Continuity mistake: There's a crumpled piece of paper on the shelves behind Peter when he argues with Walter Peck in his office. As you can observe when Peck sits down, the paper is in a different position in the close-up compared to the wider angle. (00:47:40)
Continuity mistake: The famous Twinkie scene; notice that when Egon utters the line "Let's say this Twinkie represents the normal amount of psychokinetic energy" etc, there's a cut mid-sentence. Harold Ramis is holding the bar with 3 fingers in the first shots, 4 in the second. (00:48:05)
Continuity mistake: When Winston gets the job after the very tough and thorough interview process, he walks up to Ray. Between shots, the messy cables of the traps Ray is holding are in a completely different position, and he holds the paper sheet at a different height. (00:42:20)
Continuity mistake: When Peter gets slimed, the very marketable goo stains his uniform completely messing up the right half of his chest. In the ballroom scene the uniform is practically clean on that side, but got dirtier over the left shoulder.
Revealing mistake: In the shot that follows the one with the fake cover of The Atlantic, a bespectacled Asian man walks across the street, in front of the Ghostbusters, looking prolongedly straight at the camera. (00:40:20)
Factual error: The newspapers in the 'rise to success' montage have all the dates wrong; Usa Today says Tuesday October 8, 1984 (it was a Monday), New York Post says Thursday October 22 (it was a Monday). The USA Today also has a headline "Thin Man dies" which refers to William Powell's death, in March, and the Globe cites "Princess Di expecting again!", which was announced in February (but the fake mag is dated October). (Note; the USA Today details are in the left column and need you to pause, but the others don't - you can also find perfect reproductions of the prop online). (00:39:30)
Continuity mistake: When Ray Stantz slides the trap across the ballroom to catch Slimer, the cord is curled, but it is perfectly tense in close-up. (00:37:05)
Continuity mistake: When Venkman radios Ray to tell him about the ghost, look at the cart in the background when Ray answers; the mess does not look the way it looked in the earlier close-up; there's less stuff on the partially knocked down scaffold and the table ricocheted away from the wall but here the flowers are back on it. (00:33:20 - 00:33:45)
Revealing mistake: During the montage of the Ghostbusters starting the business, there's a shot (the one immediately following the Larry King cameo), where the trio are running down a street. Many people are staring at the camera; it may seem fine since the Ghostbusters are running towards the camera, and they are celebrities so it could be argued that the people are looking at them, not at the camera. Look at the guys to the left though; they are looking past them at the camera and one of them even quickly fixes his hair. (00:40:05)
Revealing mistake: In the montage showing the Ghostbusters' rise to success, the body of the USA Today article has nothing to do at all with them, and in fact it is a copy/paste real life article that talks about Geoffrey Faux, economist. A faux article, the prop guy must have had a laugh with that. (00:39:30)
Continuity mistake: When the hotel manager says he won't pay the 5k, the trap is facing him with the top side. As it cuts to the Ghostbusters faking to just walk back in and release their catch, the trap turned 45°. (00:38:50)
Revealing mistake: When Egon tries to shoot Slimer, the wall is charred on the dark section, but the beam is shown hitting the white stucco, which bears no trace of its passage. (00:36:20)
Revealing mistake: The hotel where the Ghostbusters conduct their first sorta-successful disinfestation is supposed to be called "Sedgewick Hotel." However when the trio enters the hallway, through the window you can see the sign "Biltmore's Cleaners", and to the left "One Bunker Hill." The real hotel in Los Angeles used for the movie shoot is the Millennium Biltmore, which is in the One Bunker Hill area. (00:29:55)
Continuity mistake: Dana is at the Ghostbusters' who just tested her with a device. When she says that she does not believe in 'those things', Ego picked up a cheez-it and brings it to his mouth. In the next shot he's not the one with a snack to his mouth, Ray is. (00:23:25)
Answer: Ron Jeremy can be seen in the crowd outside the firehouse right after the containment unit is shut off.