The complex process Seth Rogen went through to star opposite himself in 'An American Pickle'

• Seth Rogen spoke to Insider about the challenges of playing two starring roles in "An American Pickle."
• It meant that he had to film the whole movie first as the character Herschel, then shave and shoot the movie again as the other character, Ben.
• In both instances, Rogen wore an earpiece that gave him the other character's dialogue and would cue his reactions and movements.
• Despite how complex the process was, Rogen said he enjoyed it and even improvised some lines.

In Seth Rogen's new movie, "An American Pickle" (on HBO Max Thursday), the actor plays two starring roles. Rogen plays an immigrant from 1920 named Herschel who — due to being trapped in a pickle vat — is preserved for 100 years and now lives in 2020 Brooklyn. He also plays Herschel's only surviving relative, Ben, who lives in modern-day Brooklyn and tries to help Herschel get accustomed to 21st-century life.

The interaction between both of Rogen's characters looks seamless on-screen. They do things together like walking around Brooklyn and hanging out in Ben's apartment.

But behind the scenes, the process to pull it off was a daunting task for Rogen every day of shooting.

Rogen says he shot the movie twice — first as Herschel and then as Ben

Rogen shot scenes for "An American Pickle" twice. He filmed all of his scenes as Herschel, growing out a real bushy beard for the part for months since he was against wearing a fake one. Then, Rogen shaved and filmed the whole movie again, this time as Ben.

The challenge was reacting to cues on set so his movements and responses would match when he played the other character.

"What's funny is sometimes you do a movie with a ton of visual effects and you're impressed by it, like the 'Avengers' movies, and sometimes you do a movie with a ton of visual effects and the goal is for it to seem like absolutely nothing is happening at all," Rogen told Insider about the lengths the movie went to make it look like "An American Pickle" was made with no visual effects.

One of the ways Rogen filmed scenes is with an earpiece so he knew what the other character was doing and saying

One element to pull off that illusion meant that Rogen would wear an earpiece that would give him the lines the other character was saying.

It would also give three beeps as a cue for when he would have to do a pre-established moment in the scene so it seemed like he was reacting to the other character.

Rogen said the scene where this was the most complicated was when Herschel is at Ben's apartment for the first time.

"I would be listening to dialogue from the other character in my ear and there would be four cues set up that I would do once hearing the three beeps for each," Rogen explained.

So in the case of Herschel and Ben toasting while drinking seltzer, Rogen said: "I'm talking, then three beeps meant I would then pick up a cup and talk, then three beeps, I'd talk more, then three beeps, he walks over there and I look over there."

On top of this painstaking process, Rogen said while playing Herschel he would sometimes improvise dialogue and then would have to make a mental note of how he would improvise back when playing Ben months later.

Rogen says he enjoyed filming this way, even though it was a technical challenge

Though it all sounds like a maddening process, Rogen said that he enjoyed it because it forced him to stay locked into the actual filming.

"Honestly, we've been making movies for so long that we're loose, I enjoyed what a technical challenge it was," he said. "I was the only other element in the scenes, so I could control how unwieldy it got at any given moment."

He added jokingly, "Who knew that the only thing I didn't like about filmmaking was working with other actors?"

Watch the "An American Pickle" trailer below to catch a glimpse of how all the hard work paid off:

"An American Pickle" is available on HBO Max on Thursday with an HBO Max subscription. You can sign up here for $14.99 per month. (When you subscribe to a service through our links, we may earn money from our affiliate partners.)