The origins of Ivan Reitman’s original Ghostbusters from 1984 is well-documented: It came from Dan Aykroyd’s family interest in the supernatural, it was originally set in outer space, it almost starred Jim Belushi until he passed away in ‘82, and the script was conceived over a boozy weekend in Martha’s Vineyard. (All pub trivia every Ghostbusters fan should know).

But as a new Ghostbusters hits theaters starring a new generation of comedians — I’ve heard they’re women — more insight into the perfect storm of the ‘84 original is coming to light. Namely, that Sigourney Weaver helped Harold Ramis and Ivan Reitman finish the script (and beat out a young Julia Roberts) by barking. There’s more in a revealing interview with Ivan Reitman from THR, but this barking bit is pretty cool.

“[T]he biggest cast member to find was the part of Dana Barrett,” recalls Reitman to THR. “Julia Roberts was one of the first. I thought she was spectacular and I turned to my casting director, saying, ‘She’s going to be a big star.’” Reitman was right, Julia Roberts did become a big star, but she wouldn’t be in Ghostbusters because then Sigourney Weaver walked in.”

Sigourney was big after 1979’s Alien, Ridley Scott’s sci-fi heart-stopper, but Reitman praised her for being “so smart” about the film’s mash-up of horror with comedy. “She said, ‘You know I really think that Dana Barrett should be possessed. She should be like that dog on the roof. And then she got on all fours on my coffee table, howling like a dog!”

Sigourney’s barking is more than just a performer’s commitment, it actually solved their scripting woes.

“I called Harold Ramis and said: ‘Harold, Sigourney Weaver just started howling like a dog in my office. She said that she should get possessed by the dog and turn into a dog,’ and I thought, Damn, that’s a really good idea.’ We had been having all this trouble about how to handle what happens on the roof in the last act, and we hadn’t solved it. Her idea of being possessed really personalized the larger concept and that got included in the script. She was barely out of my office and we were writing it already.”