Jack Cardiff came up with the idea of starting the rainfall end scene by first having a few drops hit the rhubarb leaves before cueing a full-force rainstorm. He personally created the first drops with water from a cup when the scene was shot. Michael Powell was so pleased with the effect that he decided to make the scene, originally the penultimate one, the closing shot. Cardiff, however, was a great fan of the original scene (which had already been shot) that was supposed to follow this one and close the film. To this day Cardiff amusingly calls the opening drops of the rainfall "the worst idea I ever had".
Johannes Vermeer has been mentioned as an inspiration for the lighting and color palette. A tribute to this Dutch painter can be seen in the opening scene when the Mother Superior is reading a letter, while facing a window. An image used by Vermeer in some of his most famous paintings.
St Faith (Sainte Foy in French, Santa Fe in Spanish) is supposedly a French martyr executed at Agen in Gaul (France) during the period when Diocletian was persecuting the Christians. She was tortured to death in a red-hot brazier. Her shrine is at Conques, France.
The trivia items below may give away important plot points.
Kathleen Byron strongly disagreed with Michael Powell on how Powell wanted to shoot Sister Ruth's arrival at the house of the man she loves, Dean. Kathleen Byron said, "She's very happy now she's in his presence." But Michael Powell wanted her to dart all over the place. Kathleen Byron strongly disagreed and Michael Powell walked off the set. Jack Cardiff (the cameraman) asked "Are we ready?" and Powell replied, "Ask her." Later, Michael Powell decided to agree with Kathleen Byron and he shot the scene as we see in the film. When the scene was finished, Michael Powell said it wasn't what he intended, but it was very good.
When Dean (David Farrar) puts the coat over Sister Ruth's shoulders, Sister Ruth (Kathleen Byron) sneaks a quick kiss to his hand. In an interview with Kathleen Byron at National Film Theatre, Kathleen Byron said that the kiss wasn't scripted but the hand was there and she just kissed it. Kathleen Byron also said that in a few other places she tried to play Ruth not as a totally crazy woman (as Powell often wanted) but as someone who thought herself to be sane and who, with a bit of understanding from the others, could have been helped.