When Ann is scrambling to get out of Tony's car at the red traffic light, all of a sudden the rear window is blacked out after having been seen through clearly as they were driving around previously. After Tony pulls away from the light, the rear window can be seen through again.
The newspaper report of the murder spells the word 'clue' as 'clew'. The use of the word "clew" for "clue" is old British English; a high-brow, literary spelling of the word. It is now considered archaic.
(At around 28 mins) In the closeup of Anne's hand holding a key Tony has given her, there appears to be a small hole in the thumb of her right glove. Of course, as apparel can get holes (or tears, rips, etc.) for any number of reasons (e.g., wear, accident, carelessness), this should not be considered a Goof.