Basil Rathbone was a world-class fencer and it was due to his efforts that the hilarious fencing scene was filmed without injury. He later admitted that several times he was almost skewered by Danny Kaye's sword.
The Jackson Michigan Zouave Drill Team was a U.S. Civil War re-enactment group. They performed the intricate high-speed marching maneuvers during the knighting ceremony. The US Army adopted the Model 1863 Zouave rifle, a percussion or "cap-and-ball" muzzle-loader, which was manufactured by Remington. Obviously the marching knights could not be armed with Civil War-era rifles in the movie. The original Zouave units were North African regiments of the French Army, beginning earlier in the 1800s and serving through both World Wars.
Unimpressed with him in tights, the producers made Danny Kaye wear "leg falsies" to improve the shape of his legs. This adds a touch of irony when Hubert Hawkins offers the princess all of him, including his legs and calves.
In the famous "snapping" swordfight between Danny Kaye and Basil Rathbone, Kaye's sword movements were too fast for Rathbone, who was 63 at the time. The film's fight choreographer dressed up as Rathbone's character and was filmed from behind for the fast sections. If you look, you can see that most of the fight consists of "Rathbone" from the back, then shots of the real Rathbone standing "en garde".
The "flagon with a dragon" routine had an antecedent in the Bob Hope Paramount comedy Never Say Die (1939): "There's a cross on the muzzle of the pistol with the bullet and a nick on the handle of the pistol with the blank." The credits do not list any writers in common on the two films.
Some songs that were written but not heard in the film are "I Live To Love" (sung by Danny Kaye to Angela Lansbury when he swings into her bedroom) and an extended "Pass the Basket" number when Kaye appears before the King (just prior to the famous "Maladjusted Jester"). Both songs were, however, recorded and released on the film's companion record.