Goofs

During the "AAAAAAAAAGGHH" cave scene, the actor who substitutes Eric Idle as Sir Robin (as Idle is busy speaking as Brother Maynard), suddenly vanishes between camera angle changes.

After Sir Lancelot's wedding-crashing, the bride is first seen with no blood on her face. Then a closeup shows her with bright red blood coming from her mouth and running onto her chin. In the next shot, the blood is gone again.

The blood on the killer rabbit's face disappears just after King Arthur orders the charge. It is back again in later shots

During the sword fight between King Arthur and the Black Knight, the lighting repeatedly changes between overcast and a bright sunny day, and the fire in the tent in the background changes from lit to unlit to lit.

After being attacked by the white rabbit, the knights drop their shields and run away. Sir Galahad drops his in front of the cave opening, but in the next shot, it's back on his arm. Afterward they go back to the entrance, and the knights' shields are nowhere to be seen.

Sir Galahad's coat of arms is subtly different on his shield and on his jacket. On the shield it is a 'cross fleury' whilst on the jacket it is a 'cross bottonnée'.

Tim the enchanter calls the Rabbit of Caer Bannog "...the most foul, cruel, and bad-tempered rodent you ever set eyes on!"

Rabbits are not rodents - they are lagomorphs, an order that shares a common ancestor with rodents but separated from them evolutionarily during the Paleocene epoch.

Given the fact that this movie breaks the fourth wall constantly, many crew/equipment goofs may be deliberate. In the final scene, characters even call attention to the film crew as part of the story.

Near the end of the Monks' head pounding, the monk in the foreground appears to hit himself so hard that he stumbles.

This likely is intentional, but even it not, it is feasible that a person could hit themselves such that they would stumble.

The 3 Headed Knight's voice echoes for no obvious reason. It's because it's funny.

King Arthur tells the Black Knight, "We must cross that bridge." Just behind the Black Knight for a brief moment is seen a small stream, no more than 2 feet across which could easily be stepped over. No bridge is in sight and wouldn't be needed for such a tiny stream. This is most likely a deliberate joke.

Lancelot breaks his sword during his second attack on the wedding guests, visible when he's at the bottom of the stairs.

In some shots when the rabbit attacks the knights, the string that the rabbit is moving across can be seen.

After the Scene 24 caption there's a white chicken which has been tethered, presumably to keep it in the shot.

Before the black knight loses one leg, he is slightly taller than Arthur. After losing the leg, he is slightly shorter, due to being played by a one-legged stunt man rather than John Cleese.

Whenever someone falls from the Bridge of Death, the same footage of someone falling is used.

Much of the humor in the film is based on anachronisms, given the opening title card giving the date 932 A.D. King Arthur supposedly ruled between 450 and 525 A.D. Sir Robin says he had "personally wet himself at the battle of Badon Hill" which is also between 450 and 525. Christianity did not take hold in Britain until around 600, which matches the film dating but not the legendary time-line. When confronting the Rabbit of Caerbannog, King Arthur exclaims, "Better not risk another frontal assault. That rabbit's dynamite." Alfred Nobel invented dynamite in1867.

Monk hits his head with a board before other Monks. The sound is not heard.

After Lancelot rescues Galahad from Castle Anthrax, a crew member is visible shortly after the knights go around an outside corner of the castle, just before the scene ends (toward the left side of the screen).

When Arthur reaches Castle Aargh, the camera pans back to reveal a small boat with an outboard motor on the beach.

Toward the end, when King Arthur crosses the water in the dragon boat as the land and the camera pans out, a small motorboat can be seen on the shore in the lower left corner.

The scene spoken of as Scene 24 is really Scene 13. The Bridge of Death scene (where the Old Man From Scene 24 makes his second appearance) is the real scene 24.

When King Arthur and the Knights are in the cave and reading the message in Aramaic, their heads move from left to right. Aramaic is read right to left.

In the witch-trial scene, John Cleese, Michael Palin, and Eric Idle barely restrain genuine laughter. Idle bites down hard on his scythe to remain in character.

If the members of the anarcho-syndicalist commune are taking it in turns to be executive officer for the week, but the officer's decisions are ratified on a bi-weekly basis, then there would be a different officer installed before his decisions could be ratified.

The Knights Who Say Ni are affected by the use of word "it" and end up accidentally using it themselves when begging King Arthur and his knights to stop. However, there is one brief moment prior to this where they use it without noticing or being affected (the moment when King Arthur thinks "is" is the word they're talking about).