Lotte Verbeek's character, Geillis Duncan, has the same name as a real 16th-century Scottish woman who was the first person accused of being a witch in Scotland. The whole witch trial madness stemmed from her accusation.
Ronald D. Moore praised the extras in the witch trial scenes greatly on Twitter by saying, 'Tremendous credit to all the extras who sat there on hard benches... It got hot in there and those wooden benches weren't comfy. But the extras stayed and worked hard. They're the unsung heroes of this ep'.
The witch trial scenes were filmed over an eight-day period.
Claire clearly has a BCG vaccination mark on her left arm. These were not first as standard in the UK until 1953
At one point Geilles Duncan says "Looks like I'm going to a f-ing barbecue" Later when Claire tries to stop Gillian from going threw the stones in 1968 Roger says the same thing.