Other mistake: When Theo is thinking back to when Steve offers to share the royalties from his book, Shirley is heavily pregnant with her daughter. However, on the table next to Theo, is a photo of Shirley's son and daughter, as they are in the present.
Chapter Twenty-Eight: Sabrina Is Legend - S3-E8
Visible crew/equipment: During the strobe lighting at the very end of series three, with Faustus Blackwood seemingly releasing something evil, it is noticed that during the flashes, it is leaving after effects, showing the shape of the equipment that make the strobe lighting. (00:58:00 - 01:00:00)
Factual error: Sir John Franklin, Francis Crozier and James Fitzjames all wear a crown over an anchor on their epaulettes, the rank badge for a captain with over three years in rank. This is correct for Franklin and Crozier, but Fitzjames only held the rank of commander, and should therefore only be wearing an anchor on his epaulettes.
Continuity mistake: Ruth Deaver is helping Alan Pangborn put on his tie. The camera is facing Ruth's back and we see Alan's face in the mirror. The camera then switches angles to face Alan's back and Ruth's face. Alan's collar which was popped straight up from the first angle is now perfectly down over his newly tied tie from the second angle. (00:24:55)