For his ceremony scene, actor Jung-min Hwang filmed for 15 minutes without break. It was one long-take scene.
According to director Na Hong-jin, this movie was made on the basis of folk religions in Korea and Nepal and on Catholic faiths.
No higher animals (the worm in the beginning is per definition not a higher animal) were harmed for the making of this movie. The animal scenes were done after consulting with animal trainers and under observation. The film also had a staff for VFX.
The stone throwing by white women scene alludes to An allusion to an utterance of Jesus' in John 8:7, viz. "He that is without sin among you, let him first cast a stone at her."
The prayer that Yang Yi-sam, Do-yoon Kim says when he's entering the cave is the Prayer to St.Michael.
Jun Kunimura's camera at the end of the film is a Minolta Hi-Matic S, which was released in 1978.