The role of Rocket in particular is demanding, necessitating Gunn to waddle on all fours, something his writer-director brother James Gunn has pointed out that very few actors have the physical ability to do. Rocket has a number of scene-stealing moments, but the real surprise is Kraglin, which is earning Gunn praise for bringing humor, intensity and emotion to the part.

In a conversation with Heat Vision, Gunn opens up about the demanding Guardians shoot, keeping his bigger role a secret for years, and how his brother's face told him everything he needed to know after a take.

You are a much bigger part of this movie than the trailers would let on. How early on did you learn you'd have an expanded role?

My brother James sat me down around July of 2015. He told me pretty much the whole plot of the movie. He was pretty far into the screenplay process at that point. There were maybe one or two little things that were different. He told me all of the new stuff for Kraglin, but they were spoilers and I'm not allowed to talk about any of that stuff … so I've been sitting on that information for two years, ready for somebody to see it. I think it's part of the reason I'm not in a lot of the trailers and stuff is because you don't want to know what side my character is on. I've known for a long time that the role was bigger. I've been ecstatic about it, but I've also been around Hollywood long enough know your scenes aren't in the movie until you've been [to see] the movie. Any of your scenes can get cut at any time, but I've been very fortunate. I didn't have anything cut from the movie.

It's obvious Chris Pratt and others do a lot of physical training for this movie. But when I see on-set photos of what you are doing as Rocket, that looks very physically demanding. What kind of preparation did you do?

I have my series of exercises I do. I go through stretching exercises and core exercises. I go to the batting cages. I go up and down steps a lot to keep my legs kind of strong and do crouches and stuff. I feel it, but actors are physical artists. Take care of yourself and have your body be in the right shape to do your job is part of my job.

Rocket has scenes with Kraglin. That must be tough to be playing two parts at once.

Those are long days. Sometimes we didn't have time to do a wardrobe change. Kraglin's got his jumpsuit that he wears and Rocket is in a comfortable track suit, which his nice to wear on set, but it's very hard to do much crouching in the Kraglin outfit — and I can't walk in it as Rocket. So I would have to do some wardrobe changes and we just kind of shot around me. We would shoot the scene from different points of view and I would try to do both, but there were definitely a couple of times when it was tricky. James and I were like, "What? How are we going to do this exactly?" We tried some different things but I think it all worked out.

There was one time when I'm actually I remember they were shooting and they are on Kraglin's back [the camera is shooting his back] and I'm trying to do Rocket's lines, but not moving my head so you can't tell when you're shooting me from the back. There were fun moments like that.

You and James have a shorthand from all your years together. Do you remember any times that came in handy?

For me, it comes in handy most often when I can look at his face after a take and know whether he's gotten what he's wanted or not. Generally, it's not like he looks super happy or anything, but generally if it's on to the next thing, that means he's pretty satisfied. I can usually tell. I've known him long enough that if he has any kind of grimace on his face, I know it's time to try something else.

Cinematographer Henry Braham recently joked to me that you get no slack from James on set. Are you treated more harshly on set because he's your brother?

[Laughs]. I don't perceive it that way. He'll make fun of me. He'll give me a hard time, the way he does [Michael] Rooker for sure. At the end of the day I think it's all done in the same spirit of camaraderie that he treats the whole cast.

With Gilmore Girls, you dealt with celebrity earlier on in life than James. What has it been like seeing your brother now become one of the rare directors that people might recognize on the street?

I think he likes it. And mostly because I think he's so engaged with his fans. The idea there's a face behind this creative force is something his fans appreciate and that he really enjoys. It's been weird for me. I've been sort of a low-level recognized. I've been fairly recognizable for 15 years maybe, but not ever recognized a whole, whole lot. It's really been since the Gilmore Girls reboot in November I'm recognized a lot more now, and with the movie about to come out, I can't even imagine. I’m trying to be mentally prepared.

Stay tuned to Heat Vision Monday for the second part of our Gunn interview, where we discuss spoilers that can't yet be revealed. Guardians of the Galaxy Vol. 2 is in theaters now.