Revealing mistake: When Father Karras sprinkles holy water on Regan, they forgot to paint her ear lobes and it looks terrible. (01:32:30)
Continuity mistake: When Sgt. Howie first goes to the Post Office, he walks through to where Myrtle is painting the hare. He puts down his leather case which then changes position a few times during the next few shots, until the scene ends.