'The Last of Us' stars Bella Ramsey and Pedro Pascal on the HBO hit (and those Clickers)

Bella Ramsey has a soft spot for zombies. But not just any zombies: Clickers.

In the second episode of HBO's "The Last of Us" (Sundays, 9 EST/PST), adapted from the hit 2013 video game, apocalypse survivors Ellie (Ramsey) and Joel (Pedro Pascal) come face to face with the so-called Clickers: humans who have been severely infected by a fungal outbreak and now resemble mutated, mushroom-like creatures.

"I find them fascinating," Ramsey says of the undead, who use echolocation to track their victims. "I guess it's scientifically plausible that these creatures could exist. I like how smart they are and how connected they are to each other; it's very familial. I'm probably loving on the Clickers a bit too much – every time I eat a mushroom now, I can't help but think about them."

"You feel bad," Pascal says with a grin, comparing her plight to one of his favorite films. "How you feel about the Clickers and eating mushrooms is how I feel about Nemo and eating fish."

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HBO's 'The Last of Us' isn't trying to 'reinvent' the video game

Like the game, "Last of Us" is set in the near-future United States, where a fungal pandemic has turned most of the population into powerful, predatory zombies. Using a combination of actors in prosthetics and computer-generated effects, the Clickers are nearly identical to their video game counterparts.

"What you saw (on screen) is what we were looking at," Pascal recalls of filming the zombie scenes. "It was terrifying."

Expanding the world while staying loyal to the game was important to Neil Druckmann, who created "Last of Us" and executive produced the series with Craig Mazin (HBO's "Chernobyl").

"There was never this need or pressure to make it different for the sake of making it different," Druckmann says. "We had an early conversation like, 'There's certain things that work so well in the game (that) it's hard to imagine a better version.' The Clicker is one of those things. Why reinvent it?"

Although the show adds new characters played by Melanie Lynskey ("Yellowjackets") and Murray Bartlett ("The White Lotus"), among others, the heart of the story is still the father/daughter-like relationship between Joel and Ellie. In the first episode, Joel is begrudgingly tasked with transporting Ellie, a snarky and independent young girl who was bitten by the infected weeks earlier but remains "unturned." Together, they travel across the dangerous American wasteland and fight to survive and protect each other.

"It always needs to come back to Joel and Ellie because they are the core of this journey," Mazin says. Luckily, Pascal and Ramsey have "remarkable chemistry. They adore each other and make each other laugh and take care of each other."

Pascal, Ramsey went on a journey 'parallel' to their characters

Although both actors appeared in "Game of Thrones" – Pascal as Oberyn Martell in Season 4 and Ramsey as Lyanna Mormont in the show's last three seasons – they never actually met until walking onto the "Last of Us" set. The grueling shoot lasted roughly a year in Canada, where they bonded over music and the 1988 dark comedy "Heathers."

"Only in looking back do we realize how parallel the experiences were, in terms of Joel and Ellie," Pascal says. "We didn't have that reluctance with each other, but we were definitely shy. I was born in the ’70s and have seen every terrible movie from (that era), and Bella was like, 'Um, do you like musicals?' We're, like, two people from completely different planets, but it didn't matter in terms of how our hearts were looking at each other."

Ramsey, 19, was drawn to Ellie's vulnerability, which is often masked by a sarcastic quip. "She can be so childish and immature, and then suddenly the most adult person in the room," the British actress says. "I never got bored playing her, because there's always so many layers."

Pascal, 47, was similarly compelled by the wounded Joel, who lost his daughter, Sarah (Nico Parker), at the start of the outbreak. "I don't identify as a tough guy, but I loved the idea of grief existing within such a tough exterior, and the impossible way of burying it," he says. "The map of that character's emotional journey is so beautifully drawn."

The show is more 'intimate' than other zombie stories

Given the subject matter, "Last of Us" has already drawn comparisons to AMC's popular zombie drama "The Walking Dead," which ended its 11-season run last fall. Pascal is also a fan of apocalypse thrillers such as "28 Days Later," but says this series is unlike any genre project before it.

"More than any other dystopic show I've ever seen or been a part of, this is about a relationship in a very, very intimate way," the Chilean actor says. "There's something so tiny and intimate at the center of this huge and horrifying world."

"Last of Us" drew 4.7 million viewers for its series premiere earlier this month, according to Nielsen, making it HBO's second-largest debut in more than a decade, behind only "House of the Dragon." With strong ratings, the cable network will surely want more after the show's nine-episode first season. This season covers Part 1 of the two-part game, although Part 2 could be spread out over multiple seasons.

"Our plan is to only adapt the games and not go beyond that," Druckmann says. "Craig and I have talked quite a bit about the second game and how that might be adapted, but we don't know quite how big that might be."

This article originally appeared on USA TODAY: 'Last of Us' Episode 2: Pedro Pascal, Bella Ramsey on meeting Clickers