Early in the movie when Urbain Grandier (Oliver Reed) is seen grooming his hair. It is a close-up of him supposedly looking at a mirror in the upper left hand corner of the screen, behind the viewer. Obviously there is no mirror as he consistently misses combing the more egregiously messed up parts of his hair and instead repeatedly combs the portions that are already groomed. In fact when he is done, his hair is still messed up.
(around 1h18:30) A few scenes after Grandier has been tortured by having a spike pierced through his tongue, he is shown praying despairingly, with the camera focused on his face as shot through the mask-contraption he had worn during this ordeal. The centre of focus is his mouth and tongue. As he speaks, it can be seen that there's no wound on his tongue.