EXCLUSIVE: 6 Secrets From the 'Ghostbusters' Set: Intense Stunts, Secret Cameos and Tons of...Tapioca?!

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We already know who we're gonna call, now we have some behind-the-scenes secrets about how the cast of the new Ghostbusters will handle human sacrifice, dogs and cats living together and mass hysteria.

ET was on set of the reboot and talked with Melissa McCarthy, Kristen Wiig, Kate McKinnon and Leslie Jones and director Paul Feig about everything from the "intense" action to the upgraded Proton Packs. Oh, and that cameo by none other than Bill Murray.

"I want this movie at its core to be a funny film about friendship," Feig told ET's Kevin Frazier. "That's what drove the original one. It's all about those personalities. Then, I wanted to put them into much bigger situations."

WATCH: 'Ghostbusters' Trailer Features Badass Ladies, Hunky Chris Hemsworth, and...a Slimer Cameo!

Sony Pictures

1. Meet the All-New Ghostbusters:
"My name is Erin Gilbert," Wiig introduced herself. "My character and Melissa's character, Abby, were friends when we were in high school. We both believed in ghosts, wrote a book, then went our own separate ways. I went into the sort of education-science world, and left that behind."

"I stayed a believer," McCarthy continued of her character, Abby Yates. "I don't care if people make fun of me. I believe in the paranormal, and she's ditched me to go into less confrontational waters...I'm the one that’s always believed and has worked on it my whole life."

Meanwhile, McKinnon plays Jillian Holtzmann. "I'm Melissa's lab assistant -- not assistant, partner. And I'm in charge of the machines and am basically a freak in ways you'll find out when you see the movie," the SNL star explained. McCarthy chimed in, "But a genius freak."

And Jones stars as Patty Tolan. "I work at the MTA in the ticket booth. I'm a nice one though," she said. "I care about your trip, you know what I'm saying? You might get a free token from me. That's how I do. I spread love."

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2. There Will Be No Fashion Montages:
"I think when people first heard that I'm doing an all-female Ghostbusters, I think they assume there's going to be a lot of dress-shopping montages and trying on hats," Feig revealed with a laugh. "My only goal was to make this as kick-ass as I can, and we have our ladies kicking major ghost butt."

That they do. So, how did the ladies prepare for the "intense" action scenes?

Wiig: "Boxing lessons, karate..."
McCarthy: "Thank you for saying karate. I lived in the Philippines for four years, just mentally prepping for it."
McKinnon: "Uh, I've been sitting on a couch and it shows. Lots of video games."

WATCH: Leslie Jones Defends Her 'Ghostbusters' Character After Racial Controversy Arises

Sony Pictures

3. The Proton Packs Got a Serious Upgrade: "I can carry Kate -- and, strangely, have almost every day since we started this -- easier than I can carry the packs," McCarthy admitted of the gear-heavy -- and just plain heavy -- packs. She proceeded to pick McKinnon up to prove it. "Easy as pie! Could do this all day! I bounce her when she gets upset. The packs? Take them off of me.”

The new jumpsuits, on the other hand? McCarthy has nothing but love for them.

"Listen, I'll take a jumpsuit any way I can get it," the Heat actress joked. "When I heard we're wearing jumpsuits 90 percent of the time, I thought, 'I'm finally home. I'm finally playing a character that makes sense to me.'"

"The only thing different about this from my daily wardrobe is that there's no cat hair on it," McKinnon quipped.

Sony Pictures

4. The Secret Cameos Are...Not So Secret:
We know that original 'busters Bill Murray, Dan Aykroyd and Ernie Hudson will pop up in the reboot, as will Sigourney "Zuul" Weaver and O.G. secretary Annie Potts. Still, the cast wouldn't admit to any of it -- though they did slip up while discussing the aforementioned Proton packs.

Jones: "Bill made fun of us though."
McCarthy: "Bill..."
Wiig: "Bill..."
Jones: "Bill Gates! Bill Gates came to the set."
MCarthy: "Bill Gates. Bill Nye. Bill McGillicutty, my great-uncle from Channahon, Illinois said, 'Those packs are heavy too.'"
Wiig: "Bill Hurt. Some call him William. But we're close. We call him Bill."

Feig was more open, admitting that having the original cast on set was "intimidating."

"I'm the lifelong fan of theirs and the thought of getting to work with either one of them was such a dream," he gushed over Murray and Aykroyd. "It was intimidating at first, when you knew that they were going to come...[But] it was a joy to have them there."

EXCLUSIVE: Kate McKinnon Doesn't Want to Watch Herself in 'Ghostbusters' But Knows It's Going to Be Great

Sony Pictures

5. What About That Iconic Theme Song?
Feig says he knows the theme song is "a pretty big part" of the Ghostbusters franchise, but that's about all anyone will say. Though, it did prompt this hilarious moment from the cast:

Wiig: "Kate plays the flute."
McKinnon: "It's the piccolo, thank you."
Jones: "Triangle."
McCarthy: "I play jazz sax."
Wiig: "I just spin around. I'll only be useful in the video. I just spin in circles."
McKinnon: "So, we've recorded something and we're showing it to Paul later. We'll see what he says."
McCarthy: "She does jazz triangle, [points to herself] jazz sax, [points to McKinnon] piccolo, and [Wiig spins] if she had the right shoes on, put some breadcrumbs down, you hear the crunching. It's almost percussion."
Wiig: "My percussion is me eating. Just crunching."
McCarthy: "You can just eat chips."

Sony Pictures

6. The Secret Behind the Slime:
Another big secret the Ghostbusters crew seems set on keeping is what exactly is in the lime-green goo. Feig did tell us that you can eat it -- though you probably wouldn't want to -- and exactly one of the mysterious components.

"I will tell you one of the secret new ingredients is tapioca flour," Feig teased. "And a lot of other stuff. But it's very hard to get off! I will say that. Everyone wants to get slimed and then you get slimed and you realize it's very hard to de-slime."

hits theaters on July 15, 2016.

Find out how Ghostbusters will pay homage to the original movie in the video below.