Revealing mistake: In the early part of the chase scene, when the person hanging the banner swings into the pane of glass, you can actually see it start to shatter before he touches it.
Continuity mistake: Watch the bar scene about ten minutes from the start of the film. The barmaid is holding 2 pints, but note how the froth disappears when the shot changes as they are placed on the bar.
Factual error: When Sally and Bryan are in the street, we can see, at their back, election posters. These posters appeared in 1932, one year after the movie is supposed to take place.
Continuity mistake: As Allen is preparing for his blind date, he knocks almost everything off the second shelf of the medicine cabinet, while trying to control the hair dryer. When the camera changes position, however, it's all back on the shelf. (00:21:30)