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It could be inferred from the wine drinking that the cult is heavily based off of Heavens Gate cult, in which 39 members of the cult committed ritualistic suicide. However, there seems to be potential influence from Charles Manson's cult, which originated in a time renowned for open and free love.
The director and the writers had complete creative control on the film, as it was independently produced without any involvement from major studios.
In the scene when Will recalls his son Ty's bedroom, a seemingly random assortment of toys scatter the floor, including lettered blocks. Actor Logan Marshall-Green, who plays Will, admits he left an intentional "easter egg" in this scene, which is that he used the blocks to spell out the name KUSAMA in honor of the film's director Karyn Kusama.
In Spain was released in 15 theaters / Widest release: 17 theaters. The film was only projected in subtitled version.