Hatching,” a Finnish horror movie premiering at Sundance, has two monsters at the center of its story: a grotesque bird creature and a pushy gymnastics mom.

Helmed by Hanna Bergholm in her feature directorial debut, “Hatching” follows 12-year-old gymnast Tinja (Siiri Solalinna) as she struggles to live up to the high expectations of her mother (Sophia Heikkilä) — oh, and she discovers a mysterious bird egg and secretly cares for it in her room. Over time, the egg grows larger until it hatches a disturbing, bird-like monster whom Tinja affectionately names Alli. Tinja keeps the creature hidden from her family, and the two soon grow a close bond as Alli senses the pressure Tinja is under, though the feathered freak of nature meanwhile develops a taste for blood.

“[Tinja] has hatched into the egg all her sorrow and fear of her mother seeing her unable to be a perfect gymnast,” Bergholm explained to Variety ahead of “Hatching’s” Sundance premiere. “The creature, in my mind, is a metaphor of all of she’s afraid of. This Alli creature is kind of an image of a teenager who is smelly and slimy and raging to its mother, but at the same time it wants to be hugged and taken care of.”

With the help of creature FX designer Gustav Hoegen, who has created alien species in several “Star Wars” films and dinosaurs in “Jurassic World: Fallen Kingdom,” Alli was brought to life as an avian animatronic. Over time, the feathery creature molts and transforms in unsettling ways, making it a particularly “fowl” body horror film.

However, Bergholm says Alli isn’t the scariest part of “Hatching” and that Tinja’s social-media obsessed mother is the real monster. She constantly vlogs her family’s lives, though she films a fake, picture-perfect lifestyle that eventually cracks under pressure.

“She’s more horrifying than the monster,” Bergholm says. “The monster is more of a real person, more normal than the mother. I feel sorry for her because it’s very sad to try to find happiness for yourself from external things, like buying nice things and representing a fantasy world of your life and not reaching real happiness. She’s not able to face the people and situations as they are … Unloving-ness creates a monster. She’s always smiling but it doesn’t really mean anything.”

Screenwriter Ilja Rautsi, who attended the same film school in Finland as Bergholm, brought his experience as a child gymnast to the film — but Bergholm adds “he really liked it so he doesn’t have traumas.” He originally envisioned a male protagonist for the film, and Bergholm changed it to a girl when they developed the idea.

“What I want to tell through this process of the girl facing her mother and the mother seeing all the sights of the girl she was afraid to see, it makes the girl stronger,” Bergholm says. “But you can’t live through this kind of childhood without some scars.”

IFC Midnight acquired the distribution rights to “Hatching,” and plans to release the film in theaters and on VOD platforms on April 29. After “Hatching,” Bergholm and Rautsi are staying in the horror genre with a film about young parents who welcome a troll-like baby.