Heart surgery scenes in the film are real. They were filmed during an operation on a real patient who was undergoing quadruple bypass surgery which Colin Farrell attended.
The film's title comes from the ending of the tragedy Iphigenia in Aulis by Euripides.
Colin Farrell admittedly felt nauseous after reading the script for the film.
Alicia Silverstone and Nicole Kidman were cast because they were both fans of Yorgos Lanthimos, and begged him to cast them. Silverstone later said, "I would just die to work with him again."
Though their characters are romantic interests and two years apart, Raffey Cassidy (Kim) is ten years younger than Barry Keoghan (Martin). They were 14 and 24 during filming, respectively.