SPOILER ALERT: This story contains plot details from Tuesday night’s season 3 finale of iZombie, titled “Looking for Mr. Goodbrain, Part 2.”

“Don’t be a dick.”

Seeing as that was the last line of the season 3 finale of iZombie, we were prepared to use it back to showrunner Rob Thomas when he evaded our questions about what happens to our favorite members of the undead in the aftermath of Discovery Day and Liv (Rose McIver) scratching Ravi (Rahul Kohli), possibly turning him into a zombie. But we didn’t have to use it. Much like the episode itself, Thomas did not disappoint; instead, he loaded us up with all kinds of season 4 details to help us through the long wait until Liv and co. are back on the air.

ENTERTAINMENT WEEKLY: Even though we’ve been building to it all season, I was a bit surprised to see Discovery Day, the day when humans learned zombies are real, come so early in the series. Can you talk about the decision to go there at this juncture?
ROB THOMAS: I really like thinking of each season as an enclosed story, like each one is a book in a series, and I’m so excited about what we can tell in season 4. I’m excited to get to those stories…. I don’t believe there’s any show in which zombies and humans live together in a city, and I think it’s going to be interesting. There’s so many comparisons we’ve been using in the writers’ room. It’s like zombies and humans living together in West Berlin in the middle of the Cuban Missile Crisis. Because, in the three months between the end of season 3 and season 4 begins, the U.S. government is going to wall off Seattle so it’s going to have that Berlin feeling. It sort of turns Seattle into this independent quasi-nuclear power: If zombies go flooding out of Seattle, they have the power to end the world, essentially.

That sounds really timely and intense. Is the government going to be rounding up zombies that leave Seattle?
Both Fillmore-Graves and the U.S. government would be working in conjunction to keep all zombies in Seattle. It’s in everyone’s best interest. There’s a mutually assured destruction there. And there’s going to be a No Man’s Land. So, essentially no sides want zombies to escape. And, if you’re a zombie, brains are available in Seattle; rains are not available outside of Seattle unless you kill humans or grave-rob.

What will be the brain source in Seattle?
In Seattle, Chase Graves (Jason Dohring) has told America, “Give us your brains.” And we’re going to start season 4 with a celebrity commercial reminding Americans to sign their brain donor cards. I think Chase Graves says if just one in 10 Americans donate their brains, everything is fine and dandy.

That still seems like a pretty low percentage.
I did the math on this. I actually sat down and I don’t know how good my math is, but I did rough it out with death rates and tried to actually figure out how many brains they would need. So if one in 10 Americans donates their brains, Seattle should be able to operate just fine. In fact, episode 401, the first one back, because I want to illustrate it for the TV audience, we’re going to open on a montage of how the whole brain system works, starting with a guy dying, showing the brain harvesting, showing it going on a shipping container, showing it getting to Seattle, going to a brain processing plant, getting put into to a tube, going to a dispensary, going to a Zombie With a Brain card, and being consumed. I think it’s important that the audience knows how it’s supposed to work.

Have you cast a fun cameo for that celebrity PSA?
I’ll tell you who we want to get: We want Laura Linney. She is the perfect person to help ask America for brains.

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Getting back to this episode, I so enjoyed the platonic “I love you” exchange between Liv and Ravi, but I worry there are shippers out there who will cling to that.
They are wrong.

Ha! Good. Now, are there going to be any side effects to Ravi making himself a guinea pig for his own zombie virus vaccination?
Yes, there are going to be side effects. You will see those in episode 401. We will not make you wait. You will see them right away.

With Major (Robert Buckley) in such a different headspace in this finale, it seems like we’re a long way from he and Liv getting back together, even though they’re both zombies now. Is there hope for them in season 4?
I never want to say that there’s no hope for them because I think that they would do anything for each other at any time. But they are on opposite sides of a political divide as this season moves forward, and there are going to be some political wedge issues that are forcing them apart over the course of the season. Major has found a home in Fillmore-Graves and Liv becomes in increasingly disenchanted with how Fillmore-Graves is run and what they are decreeing and how they manage the city. That is going to put them at increasing odds. It’s going to be the topic that they can’t discuss without fighting. I don’t want to imply that season 4 is going to be one long fight between Liv and Major because that won’t be the case. There’s still a lot of affection between the two and they’ll still be jokey and fun until they get on that one topic, and occasionally they will battle that out.

Can you talk about that cheeky scene showing Baracus (Kurt Evans) in a very George W. Bush-like situation, reading to schoolchildren as he receives news of Discovery Day reaching a violent head?
I don’t know what you’re talking about. [Laughs] Cheeky was exactly what we were going for…. Yeah, the nod to a certain government official — we thought we were being cute, and now, I find myself longing for George Bush, wishing we could have George Bush back in the White House and remembering him fondly. So I sort of regret making fun of that moment. It did make us all laugh in the writers’ room at the time, allowing Peyton (Aly Michalka) to be the person who whispered in his ear, recreating that moment.

iZombie will return for a fourth season on The CW.