- Dawson Casting: Barry Keoghan plays a high school student in his early twenties. He's actually ten years older than Rafey Cassidy - whose character is only two years younger than his.
- Fake American: Sunny Suljic (Bob) is the only American actor amongst the main cast, despite the movie taking place in Ohio. Colin Farrell and Barry Keoghan (Martin) are Irish, Nicole Kidman is Australian and Raffey Cassidy (Kim) is British.
- Those Two Actors: Colin Farrell and Nicole Kidman starred in The Beguiled immediately after this.
- Throw It In!: For the heart surgery scenes, filmmakers filmed a real patient undergoing a quadruple bypass.
Trivia / The Killing of a Sacred Deer