Why a movie about rats by Morgan Spurlock is the scariest thing you'll watch this Halloween

Morgan Spurlock was nine years old when he knew he wanted to be a filmmaker. But it was an unlikely movie that got him hooked.

"My parents took me to see 'Scanners' and when Michael Ironside made that guy's head explode, that was the moment I wanted to make movies, changed my life forever," an excited Spurlock recently told Business Insider while sitting in a conference room in New York City.

While perhaps not the first choice for most parents as a family outing to the movie theater, the experience nourished Spurlock's love of horror movies, which has been dormant most of his career as he skyrocketed to fame as a documentary filmmaker with his debut movie, 2004's "Super Size Me."

But now as a more established name (with numerous nonfiction features and TV shows under his belt), Spurlock can call his own shots with his production company Warrior Poets. So when he was handed the Robert Sullivan book "Rats: Observations on the History & Habitat of the City's Most Unwanted Inhabitants" late last year, he saw a way to return to his love of horror.

"I read it and I said, 'What if we made a horror documentary?'" he said.

That led to him teaming with the Discovery Channel to make the "horrormentary" (as he calls it) "Rats," airing on the network on Saturday. It's a disgustingly entertaining look at rats around the world.

Using Sullivan's book as a starting point, Spurlock expands the deep dive into the rats that inhabit every inch of New York City and shows how the rodents are dealt with (and in some cases worshiped) around the world.

"It's all true and all real," Spurlock said of his movie, "but it is shot like a horror film. We scored it like a horror film. We shoot in angles like a horror film."

The result is one of Spurlock's best films in years. He delivers an experience that is grotesque and at times funny, but is all the more horrific because you know that everything you're watching is the actual thing.

That doesn't just include the rats digging into the walls and trash bags of New York City (which Spurlock captures in all its creepiness), but we then go to Mumbai where people are hired at night to go out and kill rats with their bare hands, Cambodia where rats are caught in the country to be made into delicious meals in town, England where ferocious terriers hunt down rats with glee, and back to the US in New Orleans, where since Hurricane Katrina the rat population has increased and carries debilitating diseases.

"Post-Katrina, how the rats proliferated in that area after the flooding and the exodus of people - the fact that when the water subsided and the rat population grew is remarkable," Spurlock said. "Because it just goes to show you they don't really need us and when we are gone they will still be around."

Spurlock also travels to India where 35,000 rats live in a temple and are considered "holy" as people there believe they are the reincarnation of deceased family members.

Spurlock and his team learned about the rat temple while researching for the movie and couldn't believe what they saw.

"There's pictures of small children that have their arms in the bowls of milk drinking the milk next to the rats," Spurlock said. "So the minute I saw that, I was like, we have to go to this place."

"I thought those pictures were fake," producer/Warrior Poets COO Jeremy Chilnick said. "I thought it was totally made up."

The rat temple is just one of many can't-believe-it's-true moment "Rats" gives you. Spurlock knows when he's got a good thing, and he sees a franchise in his future.

"We always knew it would be good but I think the movie has exceeded Discovery's expectations," Spurlock said. "I think the hope is next year there will be another one just in time for Halloween."

So what's next? Bats? Snakes? Pigeons? Spurlock doesn't know yet.

"As long as we can have that roller-coaster feel we'll have something fantastic."

"Rats" premieres Saturday on the Discovery Channel.