Eyewitness - S1-E12
Continuity mistake: When the immortal who's trying to kill Tessa snipes at her in Duncan's car, his shot shatters the passenger-side window. When Duncan tails Tessa and her police escort to the safehouse, the passenger-side window is intact. (00:30:05 - 00:35:50)
Continuity mistake: When McLeod is running to jump on the tourist boat, there is a barge docked behind it. When he lands on the boat, the barge is gone. (00:17:25)
Eyewitness - S1-E12
Continuity mistake: When the police are taking Tessa to the safehouse and they spot Richie following on his motorcycle, the cop on the back tells Tessa to get down and pulls her down in the back seat. We then cut to a long shot of Richie following the car, and Tessa is sitting up on the passenger side. When the police pull over to arrest Richie, the cop in the back seat is again holding Tessa down. (00:34:30)
Audio problem: When Duncan arrives at the museum where Amanda and Zachary are stealing the book, there is no "buzz" alerting them to his presence.
Answer: In the episode "Little Tin God," Joe Dawson mentions a duel between immortals on a temple in Pompeii—just before Vesuvius erupted. Whether the two are supposed To Be connected is up for debate, but still.