Over the course of 11 seasons, Supernatural has delivered 241 episodes filled with different monsters, mysteries, and of course, motels. But the biggest mystery of the show remains: How do the writers keep coming up with new ideas?!

“We really take great pains to not retread things,” executive producer Robert Singer tells EW. “Obviously we give nods to our past mythology, but we really want to be cognizant that we’re not telling the same story over and over again. Because that wouldn’t be fun for the audience and it’s not fun for us.”

So when it comes to finding new inspiration, showrunner Andrew Dabb says, “It begins in two places: There’s the character place and the plot place. How can we evolve these characters? We’re living in a world where Sam and Dean have changed a lot over the course of 11 seasons, and where do you take them that feels natural but also feels like new ground? Specifically, this season, Mary becomes a springboard toward interesting character growth for both of them. That’s the character place, that’s leaning heavily on what’s come before, who these people are.

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“I wrote an episode a few seasons ago that applied cartoon logic to Supernatural,” Dabb says. “That was literally from watching the Looney Tunes archives. We did the Ghostfacers episode years and years ago, which was taking reality TV and applying it to our show. We’ve done sitcoms on our show. In the ‘Changing Channels’ episode, we did our version of Grey’s Anatomy. But to me, the best stuff or the most interesting stuff has something from real life in it as well. So we have a new writer on the staff this year named Davy Perez who grew up in a religious family and was able to bring, without giving away too many spoilers, is bringing some elements of that to the kind of stories that he’s writing, and I always think that’s where you get the most authentic stuff. That’s always really fun to do sure.”

Once inspiration strikes, it’s about making sure the story fits within the world the show’s established. “We certainly have rules that have been established about whatever monsters that we come up with — we have angel rules, we have demon rules, which I think you have to play within those sidelines,” Singer says. “I think some of the reason some of these shows don’t have the longevity that we have is that they burn through story really fast, where we have a slower rollout, but I also think they start playing a little fast and loose with the rules to try to get a story done and I think somehow either consciously or subliminally, the audience knows that. We have somebody who really keeps tabs on that so the rules, we try to adhere to our rules.

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“When we stub our toe sometimes is when we’re trying to create new monsters with new sets of rules,” Singer continues. “I find that those episodes are not the best. I think another thing we do successfully is our vampires or our werewolves or any of the tried-and-trues, they’re not the same character every time. We try to imbue our monsters with a story of their own and personalities of their own and an agenda of their own. In that regard, they’re not a whole lot different than any villain that you might find on a police show. Every villain is the hero of their own story and that’s something that we try to do with ours.”

And yet, no matter where inspiration strikes or how it works within the world of Supernatural, there’s one very simple rule for working on the show. As Singer puts it, “At its core, which it’s always been, it’s a story of the brothers and trying to tell interesting stories that involve them emotionally.” In other words, you can never blow off the scene where they sit on the Impala and talk about their feelings.