Jake Gyllenhaal's new children's book has a hilarious Prince of Persia Easter egg

Every actor has projects they'd rather forget — but in Jake Gyllenhaal's new children's book, The Secret Society of Aunts and Uncles, his most notorious flop gets a winking reference.

The book, which Gyllenhaal co-wrote with his best friend, Greta Caruso, tells the story of 10-year-old Leo, who loves to dance, and his clueless Uncle Mo. When Uncle Mo is tasked with watching Leo, the two end up discovering the Secret Society of Aunts and Uncles where Mo learns what it is to be a good uncle (hint: bedtime is two minutes before your parents get home, you can eat dessert first, etc.).

Gyllenhaal was inspired to write the book by his own relationship with his nieces, Ramona and Gloria (the daughters of sister Maggie Gyllenhaal and Peter Sarsgaard), but illustrator Dan Santat also stuck a hilarious nod to Gyllenhaal's career nadir, Prince of Persia: The Sands of Time. In the book, as Leo struggles to dance and fails, an audience looks on, including a skeleton holding a playbill for a show titled The Persians.

"That was Dan Santat," Gyllenhaal tells EW of the Easter egg, with a laugh. "He snuck that in before printing, and I didn't approve that. I don't know where that came from."

"Dan likes to put in his bits of humor, even misspelling my name at the back and having to put a post-it, having two A's at the end," the actor continues. "But no, when I described that space, it was the space where there was no farther down to go than the depths of where Leo is in that moment in the book. So I guess that was Dan's joke on me."

The book, which hit shelves Sept. 5, is Gyllenhaal's first children's book — but he hopes to write more. Ahead of the publication date, we caught up with the actor to talk channeling his creativity into writing, the ways his own role as an uncle and nephew shaped the storytelling, and whether he wants to see a Secret Society of Aunts and Uncles movie.

ENTERTAINMENT WEEKLY: The book is inspired by your own role as an uncle, but how did the idea first come about?

JAKE GYLLENHAAL: My best friend, Greta and I were sitting around one day, and we were discussing the idea of children's books and the idea of being an uncle or an aunt as a story that you never really get. My nieces, when they were younger than they are now — one is 16 and the other's 11, so we're not really reading much in the same way that we did when they were little kids — we'd read all these wonderful books, but none were about that relationship. No one explained what it was or what the requirements were to them or to me. So, we thought, wouldn't it be interesting to write a book about it? A children's book is probably one of the most challenging things you can do, to whittle down a very complex idea into something simple is a difficult task. Both Greta and I are people who are up for a challenge, so we decided to try our hand at it.

Was there ever a version of this story that you made up as a bedtime story or something like that?

No, but there were many versions of the story. The first incarnation of the story began as a emergency phone call to Mo when his sister had just given birth. He gets this call in the middle of the night going, "You are officially an uncle." And he gets dragged down this strange chute with thousands of other people whose siblings have just had babies, and they land on a cold floor in a darkness. That was the first idea that we had. Throughout the process I pitched it to my nieces, but it was never tried on them first.

Where did you come up with this concept of the titular secret society?

Greta and I loved the book The Magic School Bus. It was one of our favorite books as kids. We always wanted to mimic some of the ideas in that, and they always go down in the Earth to study in secret places with the bus. For us, this idea of this secret place was the beginning of this idea of a space that only existed for aunts and uncles and nieces and nephews, which is the metaphor for exactly what exists in real life, which is a very unique space that you share. But we loved the idea of dropping down to the center of things.

Part of what Mo learns there are things like letting Leo have pizza, eat dessert first, and stalling bedtime as long as possible. I'm very close with my uncle, and he would do things like tell me to get all my burps out before mom got home or take me to get ice cream if he picked me up from school. Do you have things like that with your nieces?

We do stuff all the time. We haven't done the burp thing. I mean, we've definitely burped, but not like to get all the burps out. Was it not good to burp?

No. So, he would let me drink soda and then he'd be like, "Okay, drink it really fast and get all the burps out."

Well, my big thing is I love to cook, so whenever I'm coming over, it's whatever they want to eat. They dictate it; I am their personal chef. Over the years, that's been the most fun thing for both of us. We eat whatever we want and I get to cook it. So we all get enjoyment out of it. But yeah, burping and farting are absolutely required on uncle time.

Do they have a favorite dish that you make?

It's all over the place, but generally simple stuff. A lot of times they get a lot of mashed potatoes and steak, and they like their greens too. All different things. There's not a favorite.

Did you have a similar relationship with an aunt or uncle growing up, or has it really been more you learning this dynamic as an uncle?

The book is really about both. I'm a nephew and I'm also an uncle. My uncle Bob is my mom's brother who's not alive anymore. He was a really wonderful influence. But then also, my dad has five brothers and sisters. My Uncle Max was always so playful and joked with me. My nieces tell me what an uncle is about, how to be an uncle. They get to define it. It's just about being able to see them, listen to them, and ask them how they are. They're the ones who gave me the honor of being an uncle, so they're the ones who should be able to tell me how to do it best.

Leo's passion is dance in the story. Why did you choose that hobby?

Well, there are two things. One, my oldest niece, Ramona is a big dancer. She loves dance and she's a beautiful dancer. And Uncle Mo is named after Ramona because Mo is her nickname. Gloria is my other niece's name, so that's in there too. But also dance is this thing that I find personally to be a true expression of vulnerability and your personality. It's more a common thing for all of us in that we all love to dance or are forced to dance or think we're bad dancers or think we're great at, whatever it is. It feels like a pure expression of oneself. So, we picked that as an idea, not only because Ramona loves doing it, and I've seen what a beautiful expression it is for her, but also because it is for everybody.

My uncle also introduced me to a lot of pop culture, like Star Wars. Are there things like that with your nieces that you feel like you were their gateway to a thing that they really loved now?

Oh, no. They're deeply sophisticated and more sophisticated than me and cooler than me. I didn't really introduce them to things. My girlfriend has great fashion sense, and so she introduces them to things. They always love what she's wearing and they spend a lot of time together. But for me, no, I'm more taught by them than them by me.

Did it take you a minute to get the hang of being an uncle?

That's really what the book is about. I still falter and flail a bit in it. I had this idea of what it was going to be. And then, reality hits when that beautiful being is born and all the complications of being human come into play. But then you're deeply connected. You're family. It takes time to understand yourself and to really learn how to be open and alive with that.

Do you have a proudest moment as an uncle?

I have many. There are moments all the time. Just yesterday, my brother-in-law sent a picture of both of them eating ice cream on the front of a car. My oldest niece has just come back from being with her friend and her friend's mom in Paris, and she's about to apply to colleges. My youngest niece is this incredible violinist. And I got the picture, and I was just like, "Oh, I'm so proud to be a part of their lives." They're 16 and 11, and they give me hope for the future. But it's the small things that mean so much.

Do you plan to write more books, whether it's a children's book or something else, or would you want to see this adapted in some way?

Of course. We have a million ideas, and we had to whittle them down into this one. We would love to keep going and expanding it. The process of writing the children's book, particularly working with Dan, became very cinematic for me. It is cinema in a way. You're exchanging ideas for imagery, you're changing words for image. And we worked like that. Dan and Greta and I would talk for two, three hours and we'd throw ideas around and then he'd illustrate it, and that would come up with a new line for us, and we'd have to go back to the editor and say, "Oh, can we change the text?" So it feels actually animated to me already.

How else have you been spending your time during the strike?

Well, I am actively looking to get back on stage. I love it so much. But I'm spending time with family. We've been reading and cooking. And then, writing. Honestly, I'd like to be telling my own stories and directing my own movies at some point.

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