From Insider:

Spectral Motion has been making animatronic puppets for movies and TV shows since 2002. Even if they don’t fully end up in the final shot, they can make for great references for both visual effects artists and the actors in front of the camera. Spectral Motion’s head of animatronics, Mark Setrakian, takes the characters sculpted and painted by the company’s artists and gives them the most realistic movements possible. This has included making giant troll hands compress and handle objects for “Hansel & Gretel: Witch Hunters,” manipulating robotic bits and foam skin to make a wolflike snarl for “Lady in the Water,” and making the Demogorgon’s face petals move on the first season of Netflix’s “Stranger Things.” Advancements in technology allowed Spectral Motion to push the kinds of terrifying movements it gave to the animatronic White Spike puppet who would be acting alongside Chris Pratt and Yvonne Strahovski in “The Tomorrow War.”

[Insider]