At one point a song floats over the soundtrack: "My mother, she killed me, my father, he ate me, and my little sister, my bones she kept, what a pretty bird am I!" This comes from another Grimm fairy tale, "The Juniper Tree,"widely considered by scholars as the darkest of all their tales. In it, a spiteful mother beheads her stepson and blames it on her daughter. She then cooks the corpse and feeds it to his husband, as the daughter picks up the bones from under the table and plants it under a juniper tree on the family's garden. A small bird appears from the grave, singing the song in question while picking a pair of new shoes, a gold chain and a mill stone, and then carries them to the house. The bird then gives the shoes to the daughter, the chain to the father and drops the stone on the stepmother, killing her. As she dies, the bird turns into a boy again and the story ends. The film borrows some thematic elements this tale.
The mushrooms that Gretel and Hansel find very closely resemble Fly Agaric (Amanita muscaria). When she asks the mushroom if the mushrooms are kind, she says that it says, "Eat Me" quite possibly a reference to Alice in Wonderland. The Fly Agaric mushroom contains psychoactive chemicals that can produce a wide variety of symptoms including hallucinations and synesthesia.
According to director/co-writer Osgood Perkins in an interview, the title was changed because this version focuses on Gretel, who is older: "It's awfully faithful to the original story. It's got really only three principal characters: Hansel, Gretel, and the Witch. We tried to find a way to make it more of a coming of age story. I wanted Gretel to be somewhat older than Hansel, so it didn't feel like two twelve-year-olds - rather a sixteen-year-old and an eight-year-old. There was more of a feeling like Gretel having to take Hansel around everywhere she goes, and how that can impede one's own evolution, how our attachments and the things that we love can sometimes get in the way of our growth."
The crone is never named in the movie, but the Amazon Prime feature that lists the movie's cast identifies her as "Holda".
At one point the witch in this movies says "What a world." Fans of the film The Wizard of Oz will recognize this as the Wicked Witch of the West's final words as she melts. The director of Gretel & Hansel, Osgood Perkins, often shortens his first name to Oz.