Visible crew/equipment: When the Black Knight falls from his horse while attacking Dennis there is a lorry parked in the background. (01:33:05)
Continuity mistake: When Dennis is sitting in his boat talking with Griselda and Mr.Fishfinger he gets covered in rubbish. Although he wipes most of it off there is spaghetti left on his hat and jacket. In the wide shots, though, he is clean. (00:08:20)
Continuity mistake: When Dennis first meets the man who cut his own foot off, it's because he shoved his hand (with a cup in it) right in front of his face. When the shot changes so we can look down at who it was, we see that his hand is nowhere near Dennis' face (he would have had to have been standing up and leaning over to reach his face, when we see him he's sitting down and leaning back against a wall).
Continuity mistake: When the peasant with a rock is trying to get past the two guards into the city in some shots there is a wooden pole between the guards and in other shots there isn't. (00:21:00)
Continuity mistake: In the armoury, when Dennis is trying to improve the efficiency of the riveters, the glove being riveted is only rotated in the close up shots. In the other shots they are hammering the rivets into the same hole every time. (00:46:20)
Continuity mistake: Wat Dabney's severed foot changes position on the sheet in front of him. (00:37:30)
Visible crew/equipment: When the wheel-pushing religious group are shouting about the beast, there is a modern looking box with "H2" painted on it behind the stall of an onlooker. (00:34:20)
Continuity mistake: When Dennis and Ethel are talking during the hide-and-seek competition, they are sitting next to a table with a flask on it and a sword stuck in the ground next to it. In the closeup, the sword has gone. (01:14:30)
Continuity mistake: As Mr. Fishfinger is being rescued by Dennis, some bits of rope appear on his stomach. (01:25:10)
Revealing mistake: When the Black Knight kills the King's champion with his axe, you can see the flash and smoke from the charge which blows the armour apart. (01:32:00)
Continuity mistake: While Dennis is talking with Mr.Fishfinger, a piece of straw stuck in Dennis' hair suddenly vanishes. (00:04:40)
Factual error: In the opening shot of the film, The first verse of the poem is recited. There is a very minor mistake in the subtitles on the region 1 DVD. Instead of "...in the wabe: All mimsy..." they read "...in the wabe. All mimsy...". (00:00:10)
Visible crew/equipment: During the joust, when the knight with the dog as a symbol is defeated the wire that pulls him from his horse is briefly visible. (00:43:00)
Continuity mistake: The peasant with the rock is killed by the Jabberwock. When his skeleton first lands next the Dennis, it has a bit of flesh left on it but lots of bone is visible. The shot then changes to show Dennis backing away and the peasant's corpse now has a lot more flesh on it and the legs are in a different position. (00:31:15)
Factual error: In his fight against Dennis and the Jabberwocky, the Black Knight uses a flamberge, a very distinct two-handed sword (note the little "crescent" hooks on the blade). The only problem is that these swords are a German design from the 15th century, more than 200 years after the movie is said to take place.
Factual error: The movie takes place in a Medieval European setting. This general historical context is strictly observed, but with one exception: the potato. Potatoes are part of the so-called Columbian exchange. There were no potatoes in the Middle Ages.
Visible crew/equipment: When the Black Knight falls off his horse (the same scene where you can see a truck in the background), to the right of the screen you can see a man who is wearing a modern day brown suit and a cap, standing with his hands in his pockets and watching the action. (01:29:25)
Factual error: As the knight and Dennis leave to fight the Jabberwock, another verse of the poem is recited. A line is read as "the Jabberwock with eyes aflame". The line in the original poem is "the Jabberwock with eyes of flame". (01:22:30)
Continuity mistake: Just before Dennis rescues the Fishfinger family, the knight is riding the horse that the Dog knight was riding earlier. When the Knight and Dennis are walking through the destroyed village the knight is riding a different horse. The pattern of white on its nose is very different. (01:23:15 - 01:29:35)