Real-life best friends and costars on Stranger Things, Noah Schnapp and Millie Bobby Brown now have one more thread connecting them and their characters on the show — the process of digital de-aging for flashback scenes with their characters Will Byers and Eleven, respectively.

In the first five minutes of Season 5, viewers see a de-aged Schnapp’s face on young actor Luke Kokotek portraying Season 1’s 11-year-old Will, trapped in the Upside Down and sheltering in Castle Byers with a rifle while humming The Clash’s “Should I Stay Or Should I Go.” Weta FX was behind the transformation process for Will Byers in Season 5.

This wasn’t the first time a character had been through this process which combines CGI and a younger body double. Millie Bobby Brown undertook the same task for key scenes in her character Eleven’s past in Season 4, and this work was conducted by Lola VFX. Lola did not work on Season 5.

“I asked [Millie] for help, honestly. I was like, ‘How did you work with the kid when you had to do it?’ It was fun to step into those director shoes that we don’t really get the chance to do on the show,” Schnapp told Deadline. “And think introspectively and reflectively of how I act and how I did act and move and breathe and turn and look and kind of relay that onto this little kid, who was so cute. It was a fun experience. It’s a little digital-looking. It’s hard to make it look perfect, but it turned out pretty well.”

Brown, who was “excited” to see what this would look like for Schnapp, finds the process “very interesting.” The actress shared the feeling Schnapp had of looking back to how she approached her character in Season 1.

“I was able to direct her for a couple episodes. It’s really interesting because [it] taught me a lot about what I did. I was like, ‘Yeah, how did I, why did I? Okay?’” Brown said.” I was like, ‘Wow.’ I just screamed and threw out my hand, without any sense of embarrassment. And it’s so interesting. 10 years ago, social media wasn’t a thing. It was not what it is like [now] at all. I posted pictures of my dog, and I had like 25 followers. It’s interesting, the sense of humility you really have to leave at the door.”

Brown took Martie Blair, who stood in for younger Eleven in intense scenes where viewers learned how Jamie Campbell Bower’s Henry became Vecna, under her wing just as Schnapp did with his counterpart actor.

“I really worked with the little girl I worked with in terms of, ‘It’s okay. Just like, it’s fine.’ We are going to look silly because we aren’t actually moving anything with our minds, but let’s just harness that in a superhero you have together,” Brown said. “And so I sat there behind a wall and screamed with her, threw out my hand behind camera so that she felt like she was with me.”