Warning: Spoilers ahead for "Stranger Things" season two.

Over the course of "Stranger Things 2," Jim Hopper (David Harbour) has two intense fight scenes with both Eleven (Millie Bobby Brown) and Mike (Finn Wolfhard). When INSIDER spoke with Harbour about the new season of Netflix's hit series, we asked about the experience of entering that aggressive mindset with the young actors.

"It's interesting, it was very different with both of them," Harbour said. "I had to work a lot harder while working with Millie, and I don't know exactly why. I think it's more complicated for me to yell at a young woman that way."

Hopper's argument with Eleven stems from his choice to keep her locked inside a cabin for nearly a year, all while promising she can see Mike and her other friends "soon." When Eleven realizes Hopper might not let her leave, she takes it upon herself to break out.

Eleven (Millie Bobby Brown) crying after her fight with Hopper. Netflix

Upon returning, Hopper disciplines Eleven harshly — grounding her from watching TV (her sole source of comfort and entertainment) and eating Eggo waffles. She lashes out in what the cast and crew have dubbed a "psychic tantrum," using her powers to slam doors, shove a couches into Hopper's side, and finally blowing out all the glass windows in the cabin.

"It was very emotionally complex for me to play that," Harbour said. "That was a really messed up day when we did that scene."

Hopper yelled at Eleven, scolding her for being a "brat" and not taking responsibility for the consequences of putting herself (and him) at risk of being discovered. The scene was a powerful example of two well-meaning characters clashing over a painful reality of the restrictions they're facing.

"I mean I was feeling all messed up about it," Harbour said. "But I did want to treat the scene with the respect it deserves and I wanted to treat Millie [Bobby Brown] with the respect she deserves as my female costar, and really give her my all and my power, and she’s able to give it right back. So that was a very complicated day."

Later in the season, after Mike and Eleven were finally reunited, Hopper once again had an emotional standoff with a younger character.

Hopper holding Mike (Finn Wolfhard) after he breaks down crying. Netflix

Upon realizing that Hopper had been hiding Eleven from him, Mike lashed out. He had been worried sick and increasingly more depressed, believing Eleven might be dead. He confronted Hopper angrily before collapsing in his arms and crying as he called him a liar over and over. The scene was one of the most emotionally resonant moments in season two for many fans.

"In terms of the scene with Mike, I gotta say, that was really easy," Harbour said. "I mean, look, I love all the kids equally. But as my parents would say, 'Some months one kid is your favorite and other months a different kid is your favorite,' and I have to say during that sequence, Finn [Wolfhard] really is one of my favorites."

Mike was furious with Hopper for keeping Eleven a secret from him. Netflix

"He's becoming such an interesting little artist," Harbour continued. "He's such a little weirdo. He's so into film and into storytelling, and not into the wrong things — he's really into the right things about it. So in that way I really feel a lot of love for him that I would never express to him directly but I will tell you. I just feel a lot of love for that kid."

Compared to filming his emotional scene with Millie Bobby Brown, Harbour said it was a much faster process for shooting the heated argument with Wolfhard.

"That scene was literally shot in a couple takes," Harbour said. "And it felt so quick and so easy, like 15 minutes. And the fact that the scene has resonated so much is a complete surprise to me, because it felt so natural and so easy to have that day with Finn. I'm just very impressed with him as a young actor and I think he brought so much to that scene that it was super easy to play off. It was like a gift for me as an actor."

For more "Stranger Things 2" insights from Harbour, read our interview with him about the heartbreaking meaning behind the blue bracelet Hopper wears on the show.

Sign up here to get INSIDER's favorite stories straight to your inbox.