Cosmo (Alan Tudyk): Hi, I'm Kid Cosmo.

Jason Alexander: Cosmo. 

Terry Notary: Cosmo.

Devyn Dalton: Cosmo! 

Joe Russo: One of the most important characters is the character of Cosmo.

Woody Norman: He's a very strong character. 

Millie Bobby Brown: She was Cosmo for me.

Cosmo (Alan Tudyk): You're my special friend. Kid Cosmo's your pal.

[air hissing, pop] 

Devyn Dalton: I'm Devyn Dalton, and I'm playing the role of Cosmo. I'm used to … with motion capture, lots of times you're doing things almost in a theatrical way. You'll make your movements really big. But with Cosmo, my process with it was just almost eliminating everything. Like, just letting go of the expectation of trying to be a robot and just really listen to what's happening in the scene and play off the other actors. 

Millie Bobby Brown: Devyn single-handedly helped guide me through this journey. She was Cosmo for me. She expressed so much emotion. Just the way she emotes certain things, she helped me get through so many scenes.

Devyn Dalton: I love doing regression work, which is basically, you just go back to being a kid. That's what Cosmo is. It's Kid Cosmo. It is Christopher, you know, in this new body. He's got this big head, so I'd imagine kind of the weight of this, like, really large … almost like being a bobblehead. And then having this kind of twiddly body that moves around. And when we got to see the model, he's got these cute little hips that kind of, like, flop around. 

Ke Huy Quan: They have a full-size Kid Cosmo on set for our reference, and it's just so cool-looking.

Cosmo (Alan Tudyk): My sensors are detecting high levels of fun. 

Devyn Dalton: Being a kid's pretty fun. [laughs] I don't know if you've ever seen a kid at a playground. They fall down, and you're like, "Oof." But they just bounce back up, and they're running and having fun. So it's just about kind of, like, letting go. Just being loose. Just, like, trying to relax and kind of undo anything as an adult that I have learned is really the magic  of Cosmo. 

[CLIP] Michelle (Millie Bobby Brown): Don't hurt him.

Millie Bobby Brown: During this production, you have to do one take with her and one take without her. And as soon as they take her away, I'm like, "No!" Anytime they take her away, I just imagine her and the faces she pulls, and that makes me believe in it all over again. One of my favorite things about my acting is that I get to talk to the air on occasion. It's one of my best friends. 

Michelle (Millie Bobby Brown): He gave you to Center? 

Millie Bobby Brown: But actually, I'd prefer Devyn so much more. 

[CLIP] Michelle (Millie Bobby Brown): Doctor. Doctor with glasses.

[dramatic music playing]

Christopher Markus: Kid Cosmo is in the original book. He's this little robot symbol that keeps appearing throughout the book. We loved Kid Cosmo the robot. We knew from the moment we saw him, "That little guy's going in the movie." Cosmo has a completely immobile, painted-on face. And we debated on that. I think, originally, we were all just like, "Well, yeah, no, it'll move, and he'll smile, and he'll blink." The visual effects department did a test very early on. His face had no animation. And in that draft, he also talked. And it was so moving and so affecting to see this little thing moving around and smiling, even though the physical motions were clearly sad. And suddenly, it was like, "This will be so much better if he doesn't talk, and let's just leave the face alone because somehow it's more emotional that he's got this kind of slightly psychotic grin all the time.

Cosmo (Alan Tudyk): Mission accomplished! 

Simon Stålenhag: A real human person trapped inside this pop culture surface. Yeah, I was intrigued with the fact of having a character that he has to emote through his body language. There's something about that that felt so … kind of moving.

Terry Notary: With Cosmo, it was one of the most challenging characters. And it seemed so simple, but it's not, because every look, it's the looks and the moments of suspension where you feel the inner dialogue within that character without any words. So it's a challenging character, but it's a really beautiful one, too, because it's very pure, right? It's the purest form of expression, which is expressing yourself with just looks. It's almost like the Mona Lisa. You can see the Mona Lisa in different ways. Sometimes she looks like she's smirking, and sometimes she looks like, you know, she's looking like this, and sometimes she looks very innocent, depending on how you're feeling when you're looking at the image.

Matthew Butler: The motion capture, we sort of debated as how we should go about doing this. In talking with the brothers, it was decided that they wanted to go at a faster pace, much more from the hit. So we looked into a motion capture system based on accelerometers. So instead of calculating position optically, it's recording acceleration and integrating velocity to position to work out where this thing is. So that's why you've seen people on set wearing those different funky suits, right? It's also great because now the directors can direct someone. You can see what's going on, you can frame appropriately. The editor has something to look at and cut with. So it's a real mixture. 

Anthony Russo: When we're on set, we're working with a troupe of actors. We have these motion-capture performers actually in the scenes with us. And they've spent months and months preparing physical movements that will support the creation of these mechanical creatures when the movie is finished.

Crew: Action! 

Terry Notary: When we perform on set, we're pushing to make our days, and we know that we can come back and improve on our performances. Chris and Millie don't have that luxury. We're able to take the plates from the film, and we can reenact our performances and really fine-tune and articulate the little nuances and stuff that we didn't have time for on the set. It's a win-win for everyone, 'cause we don't need a lot of takes on set. We get the takes that we really, really need for Chris and Millie's performances, so that when the brothers are happy with their performances, we're good to go. And then we can come back in the volume here and really fine-tune our side of the performance.

Devyn Dalton: The awesome thing about being here is we get to see the actual robot, so we can tell what really reads. 'Cause Cosmo has a painted face and his expression is set, it really makes a difference for me as the performer when I … you know, I do certain things to change the angle of his smile, and that kind of tells you if he's sad, or if he's questioning something, or if he's happy. So this is kind of where we get to, like, make our magic happen and fine-tune everything.

Matthew Butler: What we're doing always is inserting artificial content into production photography. So we have to completely emulate the environment if we stand a chance of integrating into that scene. If we're filming with the performer in the scene, they're gonna be, including the background, where they shouldn't be. If our robot has a hole in its chest, for instance, then we should see through to Millie Bobby Brown behind. People say things like "painting out," but there's no such as "painting out." You're "painting in," right? You're putting in what's missing. Cosmo is lifted from the book. We're grabbing as much as we can from the book, 'cause we wanna honor it, 'cause it's fabulous. So now you need to find out, "Well, who is your character?" Let's play with the motions. So now we're talking about animating. But we're talking about character and performance design. Then you've got to "look develop" it, which means, "How does it behave under light?" And you spend a lot of time finessing that such that you can put it in a scene and expect it to behave properly.

[dramatic music playing, propellers thrumming] 

[CLIP] Drone Pilot #1: Hold it right there. 

[CLIP] Michelle (Millie Bobby Brown): No! No! 

Devyn Dalton: I'm in love with Cosmo. He's so sweet. 

[CLIP] Michelle (Millie Bobby Brown): You died, and now you're here. How did this happen?

Devyn Dalton: He's dear to my heart, and I'm gonna miss him so. 

Cosmo (Alan Tudyk): Kid Cosmo thinks you are out of this world.