Revealing mistake: When Father Karras sprinkles holy water on Regan, they forgot to paint her ear lobes and it looks terrible. (01:32:30)
Visible crew/equipment: Denise arrives at her flat and finds the OAS Member there, with his back to the camera. To his right in the mirror the right half of director Fred Zinnemann's body and forearm is visible for a split second. (00:20:40)
Continuity mistake: When the guy with the snake is shot, Baron Samedi reappears and you can distinctly see the bloke holding the snake again. (01:47:00)
Continuity mistake: When Christopher Lee in drag is leading the procession towards their mini-stonehenge, look at the dolmen the villagers go through; the shadows vary significantly direction in the space of a cut.