Visible crew/equipment: When Dennis Weaver is in the cafe a shadow of a cameraman is cast across the table he is sitting at. The shot then changes to a wider angle to reveal that there isn't anyone near him who could have cast that shadow.
Plot hole: The police Inspector recounts the murders, comparing them to the ten Biblical plagues of Egypt, and he states that in keeping with this theme Dr. Kitaj was killed by rats. First, Dr Kitaj dies in a plane crash. Okay, he was attacked by rats in flight but nobody would know that - his plane crashes in a huge, violent fireball and nobody would find any rat remains after that. Second, there was no plague of rats in ancient Egypt! (Go ahead, look it up). Even if the police had made the connection between the mysterious deaths and the ancient plagues they would not make the connection here.
Visible crew/equipment: In the lower left-hand pane of glass in the kitchen cupboards, a crew member can be seen moving a rat (Ben) from the center table to where Willard left the box of rat poison. (01:30:42)
Factual error: When the judge is interrogating Margaret, a very un-18th century filling can be seen in her teeth.