Continuity mistake: In the scene where Sir Galahad is about to enter Castle Anthrax, it's pouring like there's no tomorrow. Although when he falls against the door and is about to open there is no rain, and no Niagara Falls pouring down the door. As a matter of fact, it's pretty dry on the door and almost a completely clear sky.
Continuity mistake: When the rabbit kills the first knight that is sent to kill it, the rabbit gets blood all over its mouth. However, when the knights charge the rabbit, in the shot of the rabbit watching them, the blood has disappeared. It reappears in the shots where it is slaughtering the other knights.
Continuity mistake: After Sir Lancelot has gone on a rampage at the wedding party, the bride is first seen with a clean face. Then in the close-up she has loads of bright red Pythonesque blood coming from her mouth and running onto her chin. In the next shot, the blood has disappeared again.
Continuity mistake: When the knights have built the rabbit and given it to the French they hide behind the top of the hill with woodland behind them. Then when they rabbit is launched at the you see a shot of them running uphill through clear ground.
Continuity mistake: When Brother Maynard is reading the inscriptions on the wall Sir Robin is hiding behind Sir Lancelot, but whenever there is a shot from behind the group Sir Robin disappears.
Continuity mistake: The witch's hand changes position from the shot where she is weighed to the close-up of her saying "It's a fair cop" or something like that.
Continuity mistake: When Galahad is being looked at by the two doctors at Castle Anthrax, his gloves are on. When the doctors lift his tunic to look at the injury more closely, he pushes the tunic back down with now bare hands. They are not shown removing his gloves, and he can't have removed them since he was too busy watching the girls examining him.
Continuity mistake: When the Three Headed Knight asks Sir Robin "What do you want?", you can see one of Sir Robin's minstrels puts the mouthpiece of his recorder into his mouth, but in the next shot, the music plays and he puts the mouthpiece back into his mouth a second time.