Like most live-action movies made back in the late '80s Beetlejuice was shot on 35mm film. No big deal there. Just point the camera at your actors, yell "action!" and start filming, right?
Well, Beetlejuice isn't as simple as all that.
When you're filming ghosts and snakes and violent shrimp cocktails, you're gonna need more than just a simple camera and some film.
Some of the more fantastical sequences in the movie were created using stop-motion animation. Basically, that just means that artists create a model—for example, a tiny Betelgeuse snake—and then take pictures of it, moving it slightly between each picture to create the illusion of movement.
That's how you get attacking sandworms on the planet Saturn. Or the Maitlands morphing their faces into hideous ghouls. Or Delia's sculptures crawling across the floor to trap her and Charles during Lydia's ghastly wedding.
Do these effects look as smooth and realistic to our modern eyes? Not really. But you have to remember—this was 1988. Movie studios didn't have computers that could animate realistic raccoon superheroes or bring a dead actor back to life. Filmmakers had to get creative with what they could do in camera.
Kids back then liked to call it "having an imagination."
Plus, we'd argue that, while these stop-motion sequences look a little weird, they're not so clunky and jarring that they take you out of the movie. They're pretty consistent with the quirky humor and other visuals in the film.