The procession of flagellants chant the Dies Irae, a famous thirteenth century Latin hymn thought to be written by Tommaso da Celano. Before stopping in the village they chant stanzas 1-4 and the Lacrimosa, stanza 18. These are repeated as the procession departs.
The script was initially rejected. Ingmar Bergman would end up rewriting it five times. It was only after the success of Smiles of a Summer Night (1955) at Cannes that it started to be considered more seriously.
The script is based on a one act play Bergman wrote 1953/4 as an exercise for the acting students at the Malmö City Theatre. He asked the pupils to suggest roles that they wanted to play. Based on this he wrote a few pages of monologues. After the exercise Bergman processed the material to the finished piece called "Wood Painting". "Wood Painting" has many similarities with "The Seventh Seal".
Another parody of the film happens in the Monty Python movie, "Monty Python and the Search for the Holy Grail" during which a group of "flagellants" walk through a village; only instead of using whips on their backs, they bonk themselves on their foreheads with boards.
The last two minutes of the film are pure improvisation. The actors have played the whole final scene, when Bergman saw in the sky a cloud of unusual shape. He told the troupe again wear costumes and directed a new version of the final scene in one take.
The trivia items below may give away important plot points.
The last-but-one scene in which Death is dancing away with his followers was shot when some of the actors had gone home for the day, using some technicians and a few tourists as stand-ins. Ingmar Bergman conceived the scene on the spot, and had to improvise quickly because of an interesting cloud formation that he wanted in the background.
The name of the character played by Gunnel Lindblom is never given and she speaks no lines in the film until the penultimate scene where she has the final line of the group being taken by Death: "It is finished."