Jeon So-nee in the South Korean science fiction horror series 'Parasyte: The Grey.' Courtesy of NetflixDirector Yeon Sang-ho has taken on other projects that involved plenty of visual effects work, but his latest offering, the science fiction horror series “Parasyte: The Grey,” presented a new kind of challenge for him.

“I’ve done quite a number of monster genres, but in the past, those creatures within a particular project tend to have a uniformed look,” said Sang-ho, who previously helmed the zombie horror film “Train to Busan” and apocalyptic fantasy series “Hellbound.”

“This time around, each of them are very different. So that means the VFX (visual effects) was more challenging and difficult to do,” he said at a recent press conference.

Set to premiere on Netflix on April 5, “Parasyte: The Grey” is a South Korean adaptation of the hit Japanese manga “Parasyte,” which follows a group of parasitic aliens who land on Earth and begin taking control of humans’ bodies.

READ: How ‘Parasyte: The Grey’ is different from original Japanese manga

The series, in particular, centers around Jeong Su-in (played by Jeon So-nee), who finds herself in a bizarre coexistence with a parasite called Heidi after it fails to take control of her brain.

In “Parasyte,” the infected can be easily identified because of their ability to sprout tentacle-like features from any part of their human hosts’ bodies, including the head.

“Within the body-snatching horror genre, ‘Parasyte’ is different in that the faces completely change visually… the faces literally open. So that was one of the most important things that we needed to visualize,” Sang-ho said.

The show also presented a challenge to the actors, who had to perform action scenes without seeing how they would actually look like. “I had no idea in terms of how the actual, final result was going to be compared to what I imagined as I was performing, that was a big challenge for me,” said So-nee.

“Because this was a little bit different from your typical action scenes, there were things I had to think about with the action school trainers and instructors. We had to imagine what the combat was going to be like because we couldn’t see [our opponents or their powers],” she explained.

But So-nee said she “put the most amount of trust in the final result and director.”

A scene of a parasite-infected human in 'Parasyte: The Grey.' Courtesy of NetflixDespite the challenges and intense scenes, the cast members made sure to have fun in between takes, shared actor Kwon Hae-hyo, who portrays a police detective in the show.

“The scale [of the set] was just grandiose so that required a lot of concentration, but that also means when you're off camera, you have to have fun,” said Hae-hyo, who has played supporting roles in countless Korean series, including “Forecasting Love and Weather,” “Flex X Cop” and “Wedding Impossible.”

READ: What makes Ahn Bo-hyun’s hero role in ‘Flex X Cop’ different

“[We] monitor the scenes, let off some steam and talk about the scenes. And when we have energy, we go on camera again. So I think we had good chemistry both on- and off-set,” he said.

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