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.

At one point Erin proclaims: "Books can't fly and neither can babies". Both happened in the original Ghostbusters (1984) and Ghostbusters II (1989).

The movie is dedicated to Harold Ramis, as mentioned in the final credits.

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.

The hotel where the ghosts appear is the same hotel used in the TV series American Horror Story (2011).

In some of the posters featuring Holtzman, on her proton pack is the number 2206. This is the same number as Dana Barrett's apartment in Ghostbusters (1984).

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.

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."

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.

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.

In the end credits, special thanks are given to "GB Superfan" Ryan E. Kemp who died in October 2015. Kemp had met with Paul Feig on two occasions and was positive about the prospect of this reboot.

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).

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.

Erin has a Apker Award from the American Physical Society on the wall in her office. This is a real annual award for outstanding achievements in physics by an undergraduate student.

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).

The ghost Slimer got his name in the cartoon series The Real Ghostbusters (1986). His name is not spoken in any of the movies, but appears in the credits of Ghostbusters II (1989).

Emma Stone turned down an offer to star in the movie. She stated that while she liked the script, she did not want to commit to another potential series so soon after appearing in The Amazing Spider-Man (2012) and The Amazing Spider-Man 2 (2014).

Holtzman calls Pringles potato chips "salty parabolas". The shape of a Pringles potato chip really is a hyperbolic paraboloid or a saddle surface.

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.

In an interview with 'Den of Geek', Paul Feig revealed that the first cut of the movie was 4 hours and 15 minutes long.

Was denied permission to be screened in China.

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).

Eliza Dushku was floated around as one of the members of the team with her name cropping up in some early credits works and the actress herself even dressing as a Ghostbuster for Halloween.

The four main cast members all joined the movie because they themselves were fans of the original Ghostbusters (1984) movie (and in Melissa McCarthy's case, The Real Ghostbusters (1986)).

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.

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.

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.

Holtzmann's hairstyle and glasses resemble her counterpart Egon from Slimer! And the Real Ghostbusters (1988).

As of July 2016 this film holds the title for 'most disliked' trailer ever on YouTube.

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".

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.

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.

Higgins University is believed to be named after Steve Higgins who plays the dean. Higgins is a writer and producer on Saturday Night Live (1975). Director Paul Feig denies this.

Jennifer Lawrence and Rebel Wilson were considered by director Paul Feig for roles in the movie.

Anna Faris, Alyssa Milano, and Eliza Dushku were rumored or mentioned by Dan Aykroyd as potential female Ghostbusters, before the project was a reboot.

The joke of Ed Begley Jr. being Ed Mulgrave Jr. as opposed to Ed Mulgrave Sr. is an homage to Ed Begley Sr. and Ed Begley Jr who are both actors.

Leslie mentions that Rowan's clothes make him look like Captain Kirk. Chris Hemsworth played Captain Kirk's father in Star Trek (2009).

Some scenes were filmed at the Ames family Stone Mansion at Borderland State Park in Massachusetts, where the Stone Lodge/Lake scenes for Shutter Island (2010) were filmed.

Four of the cast members, Kristen Wiig, Leslie Jones, Kate McKinnon, and Cecily Strong have been Saturday Night Live (1975) cast members. Melissa McCarthy has also hosted SNL four times. Of the original cast, Bill Murray and Dan Aykroyd were also SNL stars, while Harold Ramis was a writer for the Canadian sketch show SCTV (1976), co-starring Rick Moranis.

This will be the 4th time Michael McDonald (Jonathan the Theater Manager) appears in a movie starring Melissa McCarthy. He also appeared in The Boss (2016), Spy (2015) and The Heat (2013).

Aldridge Mansion is loosely based on the Old Merchant's House on 4th street in Manhattan, which is also a museum open to the public.

Erin wears an MIT class ring on her right hand, visible in close-ups and in another scene she wears an MIT sweatshirt.

Gertrude Aldridge was based on Lizzie Borden.

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.

A third Ghostbusters film had been stalled in development for nearly 25 years, until director Paul Feig pitched a reboot instead.

During the title sequence, there is a shot of the library of Columbia University. Parts of Ghostbusters (1984) were filmed at Columbia University.

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.

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.

In early pre-production, Anne Hathaway was reportedly considered for a role. The role was supposedly a doctor named Anna.

The motorcycle that Kevin rides after being possessed has plates "ECTO-2".

First Ghostbusters film not to be directed by Ivan Reitman.

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".

Martin Heiss' fashion sense is widely believed to be based on Paul Feig's own flamboyant fashion sense, but Feig denies this.

The extended cut runs 2 hours and 13 minutes, making this the longest Ghostbusters movie to date.

Spent over $70 million in marketing costs.

The first Ghostbusters film to receive a PG-13 rating.

First Ghostbusters film to introduce another ghost of Slimer's kind, a love interest in the form of Slimerette.

Melissa McCarthy and Bill Murray previously co-starred together in St. Vincent (2014).

Jillian Holtzmann eats Pringles potato chips as she ghost hunts. In the original Ghostbusters (1984), Venkman has an open bag of Wise chips with him when he meets Walter Peck.

The car the Ghostbusters use which Patty got from her uncle is a 1983 Cadillac funeral coach 'Ecto-1'.

Katie Dippold wrote the screenplay. She also wrote the cop comedy The Heat (2013), which also starred Melissa McCarthy.

Melissa McCarthy and Dan Aykroyd previously co-starred together in Tammy (2014).

The character name Erin Gilbert is in fact a combination of two characters played by Julia Roberts. Erin is based on Erin Brockovich (2000), Roberts' award-winning role, while the last name Gilbert 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.

Five actors who appeared as the crew in Other Space (2015), created by Paul Feig, have roles--ranging from brief cameos to major parts--in the film: Neil Casey, Eugene Cordero, Bess Rous, Karan Soni, and Milana Vayntrub.

Seward Street Station is fictitious.

A cop says Kevin looks like DC Comics' Clark Kent, alter ego of Superman, Chris Hemsworth (Kevin) plays Marvel Comics' Thor.

Kevin's motorcycle is a AMF Harley-Davidson SX 175 Aermacchi.

Melissa McCarthy and Kristen Wiig were together on Bridesmaids (2011), also directed by Paul Feig.

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.

Melissa McCarthy and Cecily Strong previously co-starred together in The Boss (2016).

Melissa McCarthy, Zach Woods, Jessica Chaffin, Michael McDonald, Adam Ray, Nate Corddry, and Steve Bannos all worked together on The Heat (2013).

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 film reunites Justin Kirk and Elizabeth Perkins of Weeds (2005). Their scenes are in the extended version only.

Kevin's last name is visible on his signed beefcake photos as Beckman, which resembles the last name of Bill Murray's character in the original movies, Peter Venkman.

The Aldridge Mansion may be named for Ghostbusters (1984) costume designer Theoni V. Aldredge.

Ed Begley Jr. and Karan Soni also appeared on TV series Blunt Talk.

Daniel Ramis: son of Harold Ramis has a small role as a Metal Head outside the concert Rowan attends.

Dominik GarcĂ­a-Lorido: as Mayor Bradley's daughter, sitting with him when Erin barges into the Lotus Leaf warning him to evacuate the city.

Paul Feig: the voice on the other end of the walkie talkie that tells Rowan to go clean the bathrooms.

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.

A number of actors from the original movie appear in this one - Bill Murray (Peter Venkman), Dan Aykroyd (Raymond Stantz), Sigourney Weaver (Dana Barrett), Annie Potts (Janine Melnitz) and Ernie Hudson (Winston Zeddmore).

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.

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.

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.

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.

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.

Kevin says "Ghostbusters, what do you want!" on answering machine, just like Janine does in the original Ghostbusters (1984) as she complains about working hard.

When Abby demands that Rowan shows himself, he asks "What form would you prefer I take?" In Ghostbusters (1984), Gozer gives the Ghostbusters the choice to "Choose the form of their destructor."

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).

The Ghostbusters (1984) Stay Puft Marshmallow Man appears in balloon form and tries to crush the Ghostbusters, before being popped by Erin's Swiss army knife.

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 film cast includes six Oscar nominees: Bill Murray, Dan Aykroyd, Sigourney Weaver, Andy Garcia, Melissa McCarthy and Kristen Wiig.

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).

The second Ghostbusters film in which Slimer is shown driving a vehicle, the first being Ghostbusters II (1989).

When Holtzmann is fighting Rowan at the Mercado hotel she beckons "Come out, come out wherever you are." which was first line of Glinda's song in The Wizard of Oz (1939).

Chris Hemsworth and Sigourney Weaver also both appeared in the movie The Cabin in the Woods (2012). They did not appear onscreen together in either film.

Ghostbusters (1984) 'Slimer' appears eating hot dogs, later the green ghost steals ECTO-1 with a female slimer going along for the ride.

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.

Charles Dance previously appeared in Alien 3 (1992) with original Ghostbusters (1984) cast member Sigourney Weaver, who also makes a cameo.

Sigourney Weaver and Kristen Wiig appeared together in Paul (2011) five years previously.

Melissa Mccarthy and Cecily Strong appear in The Boss together as well.

The cinematographer for this film, Robert D. Yeoman, frequently works with Wes Anderson. Bill Murray, who has a cameo in this film, also often works with Wes Anderson.

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