When Pendragon attacks Jack as he enters the castle (55m50s), duplicate shots are used of the same teeth creating different knights instead of one different tooth per knight. There aren't enough teeth missing from the dragon statue to account for the 5 knights.
At approximately 14:43 Garna had accidentally dropped the key into the water, but at 15:00, after Jack stops him from untying the boat, he falls to the dock with the key now clearly back in its place under his belt. He pulls the key and throws it into the water.
As Jack and the princess emerge from a secret passage, they begin to run down a steep cliff, with the castle far off behind them atop a distant mountain. Meanwhile, inside the castle, Pendragon and Garna walk a few feet to a window and spot them, approximately 20 meters below their window, on a beach.
As Jack battles the dragon, its size relative to his varies wildly shot to shot.
In his castle when Pendragon examines the broken mirror, there is a moment when we his reflection in it, with all his ghastly witches gathered behind him. They aren't in the room with him.
Although the rope is continually moving it frays in just one spot.
Trapped in a windmill by a creature Jack and the princess climb to the top where Jack makes a lasso from some rope and drops the loop over the creature's head and fastens the other end around pegs on the turning beam which connects the sails to the mill stone. A close up shows about four turns of rope around the beam then a shot of Jack looking at the creature. When the beam is next seen there's only about two turns on it. Despite the beam continuing to turn the noose doesn't tighten around the creature's neck.
The skeletons guarding Pendragon's forecourt have seams around the tops of their skulls. This is always a telltale sign that they were rented from medical schools or special effects houses and were not in fact reanimated from the dead by a magician or sorcerer.
After Jack kills the giant, the watching henchman leans against a house, which wobbles.
When Jack reaches up to touch Pendragon's outer gate his rubber sword noticeably wobbles.
The rope should just go over the window sill but is seen going over a pulley wheel.
When Jack's on the castle ramparts fighting the creatures who're advancing towards him in a > formation he has his sword knocked out of his hand.
This film was blatantly not filmed in England despite the story being set there. This is obvious due to the brilliant sunshine and bone dry ground as well as the washed out color of the trees and grass making it obvious that the exteriors were filmed in a much hotter climates (in this case, California).
When the Kraken appears and nears the two-headed giant, for a brief moment its metal supports appear on-screen.
After Princess Elaine drugs Jack, Sigurd and Peter arrive back at the boat, and the princess jumps to shore. Suddenly we see Jack strung up in Pendragon's castle, with Sigurd and Peter in a cage. No explanation is given.
At approximately 14:43 Garna, played by Walter Burke, locks the Princess in the cabin on the ship; as he turns to untie the boat he places the key to the cabin in a waist pocket or under his belt but misses his aim and the key falls out of shot.
In the opening narration, the book seen on screen has the phrase "ravished the land" printed on its page, but the narrator reading it says "ravaged" instead (which makes more sense in context).
While Pendragon is bewitching the princess, he mispronounces the word coven with a long O as in cove, when it should be pronounced with an "uh" sound as in oven. Jinx Dawson of the band Coven says it can be pronounced either way, commenting on how this pronunciation also used in American Movie (1999).