Essel (Alicia Vikander) wears bells on her shroud because during the Middle Ages, it was common for people who were considered unclean, such as prostitutes, to be forced to wear bells on their clothing to warn others of their presence. She has her hair cropped for the same reason; in medieval London and many other places, prostitutes had their hair cut short as a public humiliation and punishment.
Prior to setting out on his journey, the sash created by Gawain's mother and the three other witches has within it a carving of three runes, from left to right: Thurisaz (Giants) signifying "strong one" tool or weapon, defense or protection; Algiz (Elk) signifying protection, higher self, divinity, teaching; and Raidho (Ride) journey, vehicle, righteousness, inner compass, nobility and "the path."
The voice of the opening narration is actually the voices of director David Lowery and his wife Augustine Frizzell mixed together.
St Winifred does not appear in the original poem, but the tradition surrounding her tells that she was beheaded by her fiancé when she broke their engagement to become a nun. A healing spring arose at the spot where her head fell. Her head and body were later re-united by her brother, St Bueno.
There is an unusual looking spiral tower shown multiple times early in the film. This is a real building called "The Wonderful Barn". It is located in Leixlip, Co. Kildare, Ireland. It is a folly that was built on the estate of Castletown House by the Conolly family in 1743. While it served a purpose as a granary, it is generally accepted that it was constructed primarily to provide work for the local poor.