The image of God is actually a picture of the famous cricket player W. G. Grace. Why did they use his face? We don't know. Maybe it was the manly beard. (Source)

Terry Jones went on to write a book called "Chaucer's Knight: The Portrait of a Medieval Mercenary." While shooting in Doune Castle, he learned that there were dividing walls so the king could be defended from his own knights, who were mercenaries and couldn't be trusted. (Source)

Everyone's favorite character, Sir-Not-Appearing-in-this-Film, was played by Michael Palin's son. He's since gone on to play the same role in all other films. (Source)

Gilliam and Cleese did all their own stunts in the fight between the Black Knight and the Green Knight. They did it because it was fun to learn how to swordfight, but also because it was filmed near the end of production and they'd run out of money. (Source)

Gilliam was originally scripted to play Sir Gawain, a character who would continuously break the fourth wall. Instead, his role was condensed to Patsy, whose one and only line points out the use of a model as Castle Camelot. (Source)

Game of Thrones creators David Benioff and Dan Weiss say they were hugely influenced by the Holy Grail. (Source)