Continuity mistake: Throughout the film it has been made clear that it's Autumn and it is cold. Leaves have fallen and they are crunchy on the ground. In the scene where Father Karras is walking with the detective they turn a corner and it's summer again. The sky in the scene goes from grey to blue and the trees have re-greened as they pass a tennis court with players in their short whites. (00:43:00)
cktailgrl
18th Nov 2013