Although Harold Ramis could not make a cameo like his costars from the original Ghostbusters due to his death in 2014, you can see a bust of Harold just outside of Erin's university office near the beginning of the film.
When Erin Gilbert is giving her presentation of Quantum Physics, she writes equations on a board, one of which spells out the equation [Pa/RA(NO+RM)alS+UD1ies/Lab]com, if typing in this formula on Google you will be redirected to the official Ghostbusters website, an Easter egg present in the film.
During the 1990s, Dan Aykroyd's concept for a third Ghostbusters film revolved around the Ghostbusters traveling to an alternate, hellish version of New York City. Columbia Pictures balked at the proposed $150m budget. Ultimately, Ghostbusters (2016) ended up with a $144m budget, although inflation means it cost less than Aykroyd's proposed sequel.
After Erin comes to Abby's lab and announces that she has been fired, Abby says, 'Unlike Columbia, this institute is 100% behind us.' This is a reference to Ghostbusters (1984), where Columbia University allowed its facilities to be used for filming as long as its name was never mentioned.
The role of Patty Tolan, played by Leslie Jones was originally written for Melissa McCarthy. Paul Feig realized that Melissa McCarthy had played similar characters in his previous films, explaining "I wanted to unleash Leslie on the public in the same way we unleashed Melissa on the public in Bridesmaids (2011), with a very showy role."
Jason Reitman, son of original Ghostbusters (1984) director Ivan Reitman, was asked in an interview if he would consider directing the reboot. Reitman joked that, based on his existing work, his version of the film would just be people talking about ghosts.
At one point in the movie, Holtzmann says "they are heavier than you think" with regards to the proton packs. During the filming of the first two original Ghostbuster movies, the actors often complained about the weight of the proton packs.
In the late 2000s, Harold Ramis and Dan Aykroyd supervised a script for a third Ghostbusters film written by Year One (2009) co-writers Gene Stupnitsky and Lee Eisenberg. Bill Murray later said, in an interview with GQ, that he never read the script after Year One was a commercial and critical failure. Later, Etan Cohen wrote a draft. Aykroyd vehemently denied a rumor that Murray shredded the script. During an appearance on the Howard Stern Show, Murray admitted he had not read that draft either.
When possessed Kevin shows the Ghostbusters the glory days of New York City and summons ghosts, there's an advertisement saying "That's a big" and showing a Twinkie, a reference to Spengler's 35 feet long and 600 pounds Twinkie metaphor in the original Ghostbusters (1984).
When the Ghostbusters' early version of the proton pack fails and gets crushed by the subway train, the sound it emits is the same sound of the Millennium Falcon hyperdrive failing in Star Wars: Episode V - The Empire Strikes Back (1980).
There is also tribute to John Candy, who was originally approached to play Louis in the original Ghostbusters (1984) but turned down the part. The Dean of Higgins university, where Abby and Holtzmann work, is named Thomas Shanks. Tommy Shanks was one of John Candy's characters in SCTV (1976). John Candy is also featured in the original Ghostbusters music video.
During the climax, the number 1984 is seen on Jillian Holtzmann's Proton pack. 1984 the year the original Ghostbusters (1984) was released in theaters. It is also the year in which Kate McKinnon was born.
When the Ghostbusters open the container with the ghost for Dr. Martin Heiss, he jokingly calls the ghost "Casper" in reference to the children's cartoon character "Casper, the friendly ghost". The creators of Ghostbusters (1984) were sued by the owners of the "Casper" properties for $50 million plus the destruction of the film prints. because their logo looked too similar to their character "Fatso", a member of "The Ghostly Trio". But in 1986 the case was ruled in favor of "Ghostbusters". Nevertheless the live-action adaptation of Casper (1995) featured a cameo of Dan Aykroyd as Ghostbuster Ray Stantz.
When the Ghostbusters are driving to the rock concert, they pass the New York Public Library, where the original opens with. They also pass the "docking" area where Ecto-1 pulled out of after their meeting with the mayor in the original Ghostbusters (1984).
Even though the movie is set New York City, most of the filming was done on locations in and around Boston. These locations include Chinatown in Boston, Easton, the old South Weymouth Naval Air Station (now Union Point condo complex) in South Weymouth, Massachusetts, and the old Everett High School in Everett, Massachusetts. The set at Union Point was set out as a NY city street complete with street lights, lots of green screens and the focal point being a two story structure with a office building feel to it.
Rowan has a certificate for a Hughes Medal on his wall. This is an actual award that is given out biennially by the Royal Society of London "in recognition of an original discovery in the physical sciences, particularly electricity and magnetism or their applications".
A poster of the Boris Karloff film Isle of the Snake People (1971) is on display when the villain recreates the glory days of 1970s New York City. Such a recreation is complete with movie posters (Taxi Driver (1976)), neon signs, naughty businesses, billboards advertising products from the time period and even a sign celebrating the end of the Vietnam War.
The studio had long wanted to make Ghostbusters 3 for many years. When Dan Aykroyd was asked many times about the third film, his answer was always yes on condition that if all the principle Ghostbusters (1984) cast members including Ivan Reitman who directed the first two films return. The only main problem according to the main players was Bill Murray himself who shows lack of interest in reprising the role of Peter Venkman. However, the cast did reprise their roles in the 2009 video game, which is unofficially considered the third film that takes place two years after the events of Ghostbusters II (1989). According to Reitman, when he met Murray in 2011, Murray already had shown loss of interest when the subject was brought up although there was no script at that time. The passing of Harold Ramis in early 2014 was the final straw that two weeks after that Reitman announced that he didn't want to direct it, resulting in Ghostbusters 3 being canned.
Erin notes that her red hair dye is called "Garfield." Though she says "the President [James A. Garfield], not the cat," the cat has a Ghostbusters connection of its own: Both Bill Murray and Lorenzo Music have shared the roles of Garfield the cat and Peter Venkman the Ghostbuster.
In Trainwreck (2015), Amy Schumer's character is on a stalled subway train, standing next to Leslie Jones' character. She asks why is the train stalled and Jones says "Do I look like I work for the MTA?". In this film, Jones does work for the MTA.
Mindy Kaling mentioned the idea of an all-female remake of Ghostbusters (1984) in her 2011 book "Is Everyone Hanging Out Without Me? (And Other Concerns)." She is not, however, involved with the making of this film.
When Chris Hemsworth (an Australian actor) says "you know, an aquarium is like a submarine for fish", this could be a parody of an infamous comment made by Australian politician John Madigan at 02 February 2015 on ABC's "Q&A" program, in which he says "submarines are the spaceships of the ocean".
The character Jillian Holtzmann wears a necklace throughout the film in the shape of a U with a screw going through it. The Ghostbusters inspired Holtzmann's Screw U necklace pendant has since been created and is now being sold online.
The character name Erin Gilbert is in fact a combination of two characters played by Julia Roberts. Erin of course is based on Erin Brockovich (2000), Roberts' award-winning role, while the last name Gilbert is of course refers to author Elizabeth Gilbert, the author that Roberts played in Eat Pray Love (2010). Gilbert's book is also mentioned in the movie as well.
Ghostbusters (1984) and Ghostbusters II (1989) followed a group of four men (three parapsychologists and one civilian) who run a ghost capturing business. This is a "genderswapped" reboot, following four women instead.
At one point Jillian dances to "Rhythm of the Night" by Debarge. This song is in the key of D Major. The Ghostbusters theme song is in the key of A major, which is the Dominant Key of D Major. There is foreshadowing even in the music.
The trivia items below may give away important plot points.
Original cast members - Bill Murray, Dan Aykroyd, Ernie Hudson, Annie Potts, Sigourney Weaver and even Harold Ramis all have cameos in the movie. Early on in the movie version of Ramis can be seen in the form of a bronze bust in the hallway outside Kristen Wiig's office. Aykroyd confirmed a cameo appearance on his Facebook and Twitter pages, although the post was later deleted. Hudson and Weaver's cameos were confirmed by director Paul Feig on Twitter, after the first two cameos leaked to the press. Rick Moranis, who has long since retired from acting, was also offered a chance to cameo, but declined.
The book called Ghost From Our Past from the movie is actually available to buy on amazon and the authors are marked as Erin Gilbert And Abby L. Yates who are two of the main characters of the movie. This tie-in book is actually written by Andrew Shaffer, who is credited as 'book editor'. It is a revised version of the one seen in the movie, as it contains various references to events of the film and why the first line is not "This book is not a joke" (this line was not in the script Shaffer worked from but was ad-libbed during filming). The photo on the back is also different from the movie, but a printable dust-cover that resembles the movie version can be downloaded from the book's official site (ghostsfromourpast.com).
Bill Murray's character Martin Heiss does not die in the movie. In the movie tie-in book, "Ghosts from Our Past: Both Literally and Figuratively: The Study of the Paranormal", Heiss writes a foreword and states that the Ghostbusters are not frauds and had he believed them, he wouldn't have suffered large medical bills as a result of being knocked out of the window by a ghost.
Original Ghostbusters (1984) cast cameos: Sigourney Weaver briefly appears as Holtzmann's mentor Rebecca Gorin. Ernie Hudson, as an undertaker Bill and uncle of Tolan, Bill Murray, as Martin Heiss, accuses the Ghostbusters of being fraudsters. Dan Aykroyd, an all knowing cab driver. Annie Potts appears as a desk clerk, snapping her 1984 line, "What do you want..."
When the Ghostbusters are getting ready to fight the ghosts in New York, one of the billboard ads shows a large Twinkie with the slogan, "That's a big Twinkie." This is a direct quote of the famous line in the original Ghostbusters (1984) by Ernie Hudson.
At the end of the rock concert scene, Holtzmann grabs a guitar and smashes it on the stage in her excitement. This was improvised by Kate McKinnon on set. Paul Feig had to quickly stop her from smashing the real guitar, but liked the idea enough to allow more set-ups with a fake prop guitar.
During the exorcism scene, Patty can be seen swinging a metal tube directed towards Abby. This metal tube is actually one of the exterior pieces seen on the back side of the Delorean in the Back To The Future trilogy.
Dan Aykroyd's character, a taxi driver, says before driving off, "I ain't afraid of no ghosts." This is a nod to the original Ghostbusters (1984) theme song. He also calls the ghosts "Class 5 floating vapors." which is almost a word for word match for Ray's original description of Slimer: "A class 5 full-roaming vapor."
In an after credits scene, Patty Tolan is running through a tape player previously referenced in an electronic voice phenomena related fart gag. Suddenly, she looks up from the machine and says she thinks she's got something to the rest of the team. When they all look, she asks, "What's Zuul?" They all shrug in confusion. Zuul makes an appearance in Ghostbusters (1984) as the Gatekeeper of Gozer. He first shows up in Dana Barrett's fridge, later on he posseses her Body.
The containment unit shown near the end of the movie shows a "D. Barrett" and a "V. Clortho" on its monitor. Dana Barrett is Sigourney Weaver's character in Ghostbusters (1984) and Vinz Clortho is the Keymaster, the entity that possessed Louis Tully. As Rick Moranis has long since retired from acting, this was a way to include him in the film.
Slimer eating hot dogs from a street vendor is not only a reference to his original appearance in the first Ghostbusters (1984), but it also references Kevin's earlier drawing, which he describes as a ghost levitating a hot dog.
In the film's 3-D version, it is letterboxed and certain 3-D elements show over top of the black bars, with the exception of the scene in which Erin jumps into the portal, which fills up the whole screen. The same goes for the Blu-ray release.
Director Paul Feig encouraged improvisation among leading actors as well as having them incorporate some of their real-life characterizations into their characters. Some ended up in the film, with notable instances include the ladies responding to the haters and trolls after their first ghost bust video on Youtube; Abby (Melissa McCarthy) likes the film Road House (1989), which in real-life is one of McCarthy's favorite films; at the end of the film in a deleted scene Jillian mentions that Erin and herself are dating: this indicates that she is a lesbian, which Kate McKinnon actually is in real-life.
Bill Murray's character Martin Heiss is a skeptic and debunker of paranormal activity. His character of Dr. Peter Venkman in the original movies was a scientific charlatan who also did not believe in ghosts until he saw one personally. By contrast, all of the new Ghostbusters consider themselves serious scientists who believe in paranormal phenomena.
In an October 2015 Entertainment Weekly article, Dan Aykroyd confirmed that the film's cameo appearances by the original cast have them playing different characters. This is in line with director / co-writer Paul Feig's comments before filming, in which he stated that he did not want to make a film in a universe where people were already used to seeing ghosts (such as the "original" Ghostbusters (1984) timeline).
Ernie Hudson makes his cameo appearance at the end of the movie - playing Patty Tolan's uncle - outside the original Ghostbusters firehouse. In Ghostbusters (1984), this is where his character Winston Zeddemore makes his first appearance.
In the original Ghostbusters (1984) the Traveller appears because Ray pictured the Stay Puft Marshmallow Man. As Holtzman is being crushed by the inflatable Stay Puft Marshmallow Man, she mentions that this is exactly how she pictured her death.
During the end credits, Holztmann says she's made some new Ghostbuster equipment. She then says she doesn't know where the ghosts are after they are captured but she thinks it might be Michigan. Paul Feig is from Michigan.
The much maligned first trailer opened with a piano version of the Ghostbusters theme. The opening notes of the same recording are heard when Kevin, possessed by Rowan, propels a grand piano at the Ghostbusters.
When Patty slaps the ghost out of Abby, Abby say, "That's going to leave a mark." She is possibly quoting John Candy from Spaceballs (1987). John was originally going to play Louis Tully in Ghostbusters (1984) before the movie was delayed and recast.
While closing the portal, two Ghostbusters rescue the other two by pulling then back from the "other side", by pulling them on a rope. While being pulled through, their hair turns white. This is very similar to the scene of rescuing the little girl in Poltergeist (1982).
Near the end of the film when Rowan becomes a giant ghost, his face bears a very strong resemblance to Ray from the original movies. In Ghostbusters (1984) Ray accidentally thought of the Stay Puft Marshmallow Man during a similar scenario, and he is also considered the heart and soul of the Ghostbusters team.