Continuity mistake: After Chris is startled by the exploding flame in the attic there's a shot of a priest carrying flowers across a courtyard into a chapel. When he first opens the door to the chapel he's in the shade, but when we see him walking into the chapel from the other side of the door the sun is shining. (00:31:30)????
Continuity mistake: After the exorcism, Regan's wrists are tied together, but are then later seen tied to the bed.