Continuity mistake: When Arthur is out hunting in the woods, Arthur is lying on a tree branch. In one shot, his pants leg is coloured brown, whereas, in the next shot, it is skin colour (as if he isn't wearing any pants). In the next shot, the brown pants leg has returned.
Continuity mistake: When Pelinore enters the castle, he takes the glove off his left hand. When he's passing Wart, however, his right hand is the one that is bare. Immediately afterwards the bare hand switches back to his left.
Other mistake: Merlin says, "Man will fly someday". For a few frames after he says this, his thumb on his pipe is painted blue, then returns to its normal color. This causes a blinking effect.
Deliberate mistake: When Arthur is drawing letters of the alphabet, he only draws the outside of the letter A, not the horizontal stroke in the middle, yet it appears on the blackboard.
Continuity mistake: As a squirrel, Merlin's glasses come off & suddenly, it has ear pieces on the frames. When he places them back on, they're gone.
Continuity mistake: When Merlin is thrown in to the armor under the water as a fish, his glasses are thrown off and they land on the nose of the armor. The next time they show him, the glasses are down beside him. And still again, when Merlin is changed back into a human, he has the armor on his head and when he pulls it off, his glasses are on underneath the armor.
Suggested correction: Notice the dialogue just before Merlin turns himself and Arthur/Wart into fishes: Arthur: You mean you can turn yourself into a fish? Merlin: After all, I happen to be a wizard. If Merlin has the magical powers to turn himself into a fish, perhaps a by-product of his magic is that his glasses are magic, so he retains his glasses when he undergoes the transformation into a fish, even if his glasses fall off, they magically return to him, and his glasses magically reappear when he turns back into a human.
What's more likely - the director intended Merlin's lore to include magically retaining his glasses, or the team of animators made a couple continuity errors?
Continuity mistake: Arthur jumps over an enclosed fence to get to the Sword in the Stone. After he gets the sword, he runs out of an opening in the fence that wasn't there when he entered the area.
Continuity mistake: Merlin slides down the hill & skips across the water. As he crosses the water, there are a few large rocks in the water in the background. As Arthur skips across the water, there are no rocks in the water.
Continuity mistake: When the wolf slides into the water, after Arthur and Merlin, a big rock appears in the middle of the pond, that wasn't there when Merlin and Arthur crossed.
Continuity mistake: The letters A and B on the bottom row on the blackboard differ styles between shots, being wobblier in the second shot.
Continuity mistake: Before Kay cuts the mop's handle, the mop is dark brown. After he cuts it turns to vanilla coloured.
Continuity mistake: When Merlin searches for the model plane the knot holding it swaps from neat to crappy between shots. (00:56:02)
Continuity mistake: When Ector and Kay fight, the mallet behind turns 180ยบ. (00:49:30)
Continuity mistake: Arthur is seen looking at the birds flying with a pipe. In the next shot, the pipe in Merlin's hand has gone.
Continuity mistake: When the movie ends, the way the curtain on the right folds changes between shots.
Continuity mistake: The teapot with the flower at Mim's place keeps swapping back and forth between being next to the window and sitting on the centre of the windowsill.
Continuity mistake: The position and pattern of the playing cards on Mim's table keeps changing in every single shot.
Continuity mistake: At Madam Mim's, the cup and saucer on the table moves around between shots.
Continuity mistake: When Arthur is scrubbing the cauldron, a pot next to it disappears and reappears between shots. Also, the grip of the handles of the bucket behind him swap between round to square.
Continuity mistake: When Merlin arrives from the future, he talks about it to Arthur and puts the crown on his head. The sword, resting against the throne, appears and disappears randomly all the time.