For his ceremony scene, actor Hwang Jung-min 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.
Exorcism scenes by the Japanese Man stem from Shamanism in Nepal.