The science of Star Wars: How filmmakers made alien creatures believable

(CNN)When director Rian Johnson visited Ireland's Skellig Michael, where Luke Skywalker made his self-imposed exile in "The Last Jedi," the craggy island was so overrun with puffins he had to take care not to step on them.

Instantly he knew the island, called Ahch-To in the film, would also be home to the Star Wars version of puffins, called porgs.
It's the great not-so secret sauce behind the appeal of creatures in Star Wars. The alien species on the screen intrigue but don't overwhelm the human imagination because they're rooted in familiar animals we know on Earth. And the diversity of creatures matches the variety of planets in the Star Wars galaxy -- as much as it does the environments on our own planet.
"It's the scale of characters, telling a visual story of the environments, locations and geographical places on our world," said Neal Scanlan, creature supervisor on the four newest Star Wars films. "It's important to do that because it makes us feel like these worlds aren't so different from our own. This is one aspect of Star Wars that makes it really engaging."
    Many of the creatures on screen rely on a mash-up of multiple known species, as well as the sounds of those species.
    George Lucas envisioned an organic soundtrack for his Star Wars universe from day one. Sound designer Ben Burtt was tasked with creating the signature sounds of Chewbacca as one of his first assignments. He recorded bears, dogs, lions, tigers and walruses, editing their sounds together to make phrases out of them that sounded sad, cute or angry. Chewie's varying and slightly musical "waawaawaa" sounds act like his sentences of dialogue.
    Animals and creatures in the Star Wars films are a mix of practical -- relying on puppets, animatronics or people in suits -- or digital recreations.
    Neal Scanlan and his creations for "The Force Awakens."
    Some of the first creatures seen on screen in the original Star Wars film later named "A New Hope" are banthas and dewbacks. The bantha was actually a female Asian elephant wearing a head mask, palm fronds and tubing to stand in for the curved horns, according to "The Moviemaking Magic of Star Wars: Creatures + Aliens." The dewback was a puppet made from the body of a stuffed rhinoceros, fitted with a reptilian head and tail.
    New creatures await viewers in "The Rise of Skywalker," in theaters this week. They'll be joining a long and established universe of creatures such as Chewbacca that have appeared throughout the franchise. Some may appear on screen for a few seconds, while others will take a little more time to introduce themselves.
    Regardless, each creature has an entire history attached to them. And this is how it's been done for 42 years.

    Star Wars creature design: A rulebook

    When creating a creature from the ground up, the conceptual designers of Star Wars often ask this question: How would you feel if you saw this thing in real life?
    They want it to be grounded in biology and obeying the laws of nature, to a degree.
    "We're hoping that you feel you could look out your window and see a porg in your tree and not scream and think an alien arrived," Scanlan said. "Instead, it would be sort of OK that it sat in the tree."
    Humor is another key component. Much like the droids of Star Wars, the creatures can pop up and provide comedic relief -- especially porgs.
    "It should have a touch of humor about it," Scanland said. "This is also true in the way we perform the characters because we don't only try to make them feel totally real. If they take themselves too seriously, it doesn't work."
    Scanlan compared it to the success of the Muppets. No one believed Kermit was real, but he had real qualities that people could connect with and enjoy. Lucas himself was inspired by the Muppe