The following interview contains SPOILERS for Toy Story 4. And Toy Story 3. And the Pixar Theory. But mostly Toy Story 4.

For the last 25 years, the Toy Story series has demonstrated an unwavering commitment to being as emotionally devastating as possible. From Jessie’s heartbreaking backstory in Toy Story 2 to saying goodbye to Andy in Toy Story 3, no franchise that’s supposedly for children has been as consistently melancholic, and even philosophical.

That streak continued with this summer’s Toy Story 4, another animated romp slash soul-crushing tale of broken dreams from the men and women of Pixar Animation Studios. One of the men in charge this time is Mark Nielsen, a longtime Pixar contributor who produced Toy Story 4 after working on films like A Bug’s LifeMonsters Inc., and Inside Out. When we spoke on the phone last week, I asked Nielsen how Toy Story evolved from a buddy toy comedy into an ongoing meditation about mortality, relationships, and lost opportunities.

“Part of it is time,” Nielsen explained. “We’ve spent 25 years, if you’ve been with it from the beginning, with these characters and when you’ve been through thick and thin and watched them face the fire together, and go through all these ups and downs, you connect with them and they feel like people you might know. I also think there’s deep-seated in everybody this belief from their childhood that toys potentially are these friends, and are maybe alive when they left the room. And the receipt to that was really how successful these films have been.”

In fact, Toy Story 4 was the most successful film in the franchise to date, grossing more than $1 billion worldwide, and now it’s available on Digital HD and Blu-ray. With the movie coming to home video, I talked to Nielsen about the reaction internally at Pixar to Toy Story 4’s success, the drastically different alternate endings the movie could have had, and an interesting portion of the Blu-ray commentary where Nielsen and director Josh Cooley discuss how the movie dismantles the famous “Pixar Theory” that all of the studio’s productions exist within a shared universe.

What��did you think about the reaction to the film when it was in theaters? Did anything about it surprise you?

It definitely surprised us. We were thrilled, but you never know. We don't know within the studio what the reaction's gonna be and there was a lot of skepticism about a fourth film being that Toy Story 3 really for a lot of people felt like “The End.” So a lot of people came in like “Wait, do we even need this one?” So we knew we had to be able to answer that with the film itself, and we put a lot of pressure on ourselves to do that. But you never know until it comes out whether or not you've succeeded at striking a chord with audiences. So we were very surprised and delighted at the response.

Watching the movie on Blu-ray again this week, I was reminded how accurate, for lack of a better term, Bonnie feels. I have a daughter right around her age, and I was blown away by how much Bonnie reminds me of her; the way she moves, her expressions, even the way she dresses. Who deserves credit for the authenticity of that character?

The animation team — you’ve got to credit the voice talent, Maddie McGraw is awesome — but the animators are bringing the other side of the performance to the table, which is her movement. There’s a lot of parents that are working within the animation department that took on a lot of those shots that have kids that they observe. Our animators are so brilliant at doing their homework and just digging deep into the truth of kid movement. So I credit a lot to the animation team.

Pixar

Looking at other franchises, I don’t see many that are as willing to change the characters, push the characters, the way Toy Story does. Toy Story 3 completely alters the world of those films, and then Toy Story 4 does it again. Is there ever any trepidation from Disney about these risks you guys are taking? Do you ever get push back on some of these bold ideas?

We haven’t really gotten much pushback, but I do think the filmmakers we have at the studio, and the filmmakers we have as our creative executives — I think of Andrew Stanton, for example. I can’t count how many times I’ve heard him in braintrust meetings say the words “Make me care” as one of his notes. If he doesn’t care, and it’s not emotionally affecting him, he’s just going to let you have it. And he’s one of the creative executives that drive these things. And he’s right! We’re trying to make stories that people are going to care about, and are emotional and impact them. That is our goal. Those are the types of films we love.

So I think a lot of that can be traced to Pete Docter, to Andrew Stanton, to Lee Unkrich, to those who are leading the studio, who have been making films here for a long time, and their desire to not just make another adventure, not just make another movie, or to add to the collection, but to make something that is going to be emotionally impactful, whatever it is.

I listened to the commentary track that you and Josh Cooley did on the Blu-ray, and you were talking about the antiques shop where much of the second half of the film is set. I’m paraphrasing here, but you were joking about how the goal of that location, because of all the Pixar Easter eggs in it, was to destroy the Pixar Theory.

[laughs]

And then I think in the next scene, Josh jokes that Bonnie’s mom is reading a book called Debunking the Crazy Theory of a Shared Universe.

Yes! Yes.

Now you guys are clearly having some fun there, but I was wondering whether the Pixar Theory did come up during the development of the movie, and what you think about the idea that all Pixar movies exist within a shared universe.

You know, it’s funny. We’ve never taken those ideas very seriously, and we know where a lot of it stems from. We were kind of hoping to debunk it a little bit, we did talk about it a little bit, but that wasn’t a real strong intention going into it. The truth is, what leads to a lot of these theories is the fact that we’ve reused characters and sets from previous movies for efficiency’s sake.

Right.

If you’ve got stuff that already exists, you’re going to just use it instead of building something new, because it’s going to save you time and money. That’s led to us putting a lot of things in films that are from previous films. Without knowing that, if you’re going to look at it, you could read intentionality there that’s not really there. That’s really what’s happened over time.

There’s a girl in Toy Story 4 that looks exactly like Boo because we probably we took that character from our “backlot” and used a character that was based on the Boo model. So we had to ask ourselves “Do we change her out so that she doesn’t look like Boo? Or do we embrace it because it’s kind of fun and people are actually going to think that it might be Boo, and then it’s going to spin out some more theories?” So we do get a kick out of it, and we are entertained by those theories. Sometimes it is fun for us to mess with those theories, even with the things that we are folding into the background.

One other thing you touch on in the commentary is the long development process for a film like Toy Story 4, and the fact that the story evolved over time. Was there ever a point during that writing process that Woody didn’t leave with Bo? Was there a version of the film where he went back home with Bonnie?

Yeah, there definitely was. We had versions where Woody went back to Bonnie’s house and Buzz and Woody didn’t split up. We had a version — and we have a deleted scene included on the Blu-ray — where Woody reunites with Bo, and it’s beautiful, but then he lets her go again because she makes a connection with a little girl in the antiques store and he can see that it’s better for her to go with this girl than to go back to Bonnie’s with him.

We did play out a lot of versions of this ending that were not the one we ended up with. What we realized at the end of the day was that this is Woody’s story, he is the protagonist here, and we have to affect him in a way where he’s going to experience real change. And any version of the movie we did where he went back to Bonnie’s made it feel like he didn’t really change that much; that Bo had an impact on him, got him to think differently, but then he’s sort of just right back where he started.

That’s what led us to go “You know what? I think we need to make a bigger move here.” That’s when we started exploring the idea of him going with Bo to seek a greater purpose of instead of being there for a kid, finding a way to be there for all kids. And that was like a lightbulb going off.

Gallery — The Coolest Toy Story 4 Easter Eggs: