SAN DIEGO — The zombies are adapting on “The Walking Dead.” The fourth season trailer debuted at Comic-Con showed off a breed of stronger, savvier undead — or “walkers,” as they're called on the hit AMC zombie apocalypse series — encroaching on the survivors at their prison enclave. “It's going to get insane very quickly,” new show runner Scott Gimple said. “The Walking Dead” producers were joined by such cast members as Andrew Lincoln, Danai Gurira and Norman Reedus. In the footage shown at the pop-culture convention, the survivors' barricaded headquarters have been further fortified. However, increasingly more hordes are bombarding the gates, and they're not spreading out anymore. “Yeah, the walkers are no threat at all this season,” joked executive producer Gale Anne Hurd after panel moderator and “Talking Dead” host Chris Hardwick suggested the zombies were simply animals. The clip also teased a catastrophic event inside the prison with multiple deaths. At the end of the trailer, Reedus' Daryl is shown driving a car and overhearing a voice on the radio whispering, “Those who arrive survive.” “The Walking Dead” creator Robert Kirkman said the villainous Governor played by David Morrissey will return in the fourth season but when, how and why will be a mystery that runs throughout the season. “You've just gotta be on my side. If you're not on my side, you've gotta go,” said Morrissey of his cutthroat character. “That's the deal with the Governor.” Several fans suggested to the panel what they'd like to see in the new season, including Rick and Michonne hooking up and Carl offing the Governor. The fourth season will debut Oct. 13. Game of Thrones It's wasn't hard for “Game of Thrones” to say goodbye to several characters at Comic-Con. The panel for the fantasy HBO series kicked off Friday with an “in memoriam” segment set to Boyz II Men's “It's So Hard to Say Goodbye to Yesterday.” The tribute was dedicated to the scads of characters who've bitten the dust on the show, ranging from Khal Drogo to Wine Merchant to Catelyn Stark, the character played by Michelle Fairley who died in the infamous “Red Wedding” installment. “I knew how many years I signed for, so I knew what was coming,” said Fairley at the pop-culture convention. The vicious slayings of many Westeros residents in the third season surprised many viewers, especially the brutal “Red Wedding” episode. “We'd been waiting for it for so long and dreading it, and having it turn out better than we expected because of these actors was one of the greatest moments of my life,” series co-creator David Benioff said. “Game of Thrones” cast members Fairley, Peter Dinklage, John Bradley, Kit Harrington, Rose Leslie, Richard Madden and Emilia Clarke joined “A Song of Fire and Ice” mastermind George R.R. Martin and series co-creators Benioff and D.B. Weiss. Martin said he needed to get to work finishing the two upcoming novels, “The Winds of Winter” and “A Dream of Spring,” because the show is catching up with source material. The crowd inside Hall H in the San Diego Convention Center shrieked when Khal Drago actor Jason Momoa stomped on stage and planted a smooch on Clarke, who continues to play his love interest Daenerys Targaryen, the Mother of Dragons, on the show. Momoa screamed into the microphone, “I'm not dead, George!” Marvel's Agents of S.H.I.E.L.D. Fans expecting to see a snippet of the new “Marvel's Agents of S.H.I.E.L.D.” television show Friday at Comic-Con got a surprise instead — the chance to see the entire debut episode. Thousands of fans went wild when Marvel executive Jeph Loeb and series creator Joss Whedon surprised them with the episode, which features Clark Gregg as Agent Coulson, the S.H.I.E.L.D. agent everyone thought died in Marvel's recent blockbuster film “The Avengers.” “I've got to say it's a little hot in here,” Loeb said, taking off an over shirt to reveal a T-shirt with the words “Coulson Lives” on the back. The crowd started chanting “Coulson! Coulson! Coulson!” That was just the beginning of the cheers, laughs and even tears — from Gregg, who got choked up when talking about the chance to return to the Marvel universe after appearing to die in a key moment in “The Avengers.” “I'm a longtime Marvel fan and I can't believe this is happening to me,” Gregg said as he got a little misty after hugging Whedon for an uncomfortably long period of time. “I didn't like being dead, but I really liked my death. And then I met Lola.” “Lola” is Agent Coulson's suped-up red Stingray Corvette that's not quite as vintage as it looks. Without revealing too many details to ruin the debut for fans not at Comic-Con, the show follows Coulson as he builds a team of fellow agents to deal with the growing problem created in a world quickly changing because of superheroes and their foes, alien visitors and Norse god appearances. Fast-paced and full of comic moments that don't always require a deep knowledge of comic books, the episode laid the groundwork for the series with several subplots that will play out over time. Until Friday, little had been revealed about the ABC show set to debut Sept. 24. Most of the show's cast attended, including Ming-Na Wen (Agent Melinda May), Chloe Bennett (Skye), Iain De Caestecker (Agent Leo Fitz), Elizabeth Henstridge (Agent Jemma Simmons) and Brett Dalton (Agent Grant Ward). Dalton got a wolf whistle from the crowd, leading to laughter. “Yeah, we've got a really unattractive cast,” Loeb joked.