Deliberate mistake: At the elephant graveyard, little Simba claws Shenzi in the face. When Mufasa saves Simba from the hyenas, the cuts are gone, a few seconds later. [This was done intentionally, I'm sure, for two reasons. The first being, Disney doesn't let fresh scars linger on the screen too long. Secondly, during that same scene when Mufasa rescues Simba & Nala, he claws Banzai in the rear. To stress the point later in the movie, that severe scar is shown too, but only briefly, it too disappears because of reason 1. Still a "mistake", but there's why.] (00:21:50)
Continuity mistake: Nala's eyes change from blue to green quite often during the movie.
Suggested correction: Her eyes were green the whole time. It's just lighting making it look like they changed color.
The correction assumes these lions are filmed, but they are drawn. So if the eyes are blue, they coloured it blue and if it's green they coloured it green, on purpose.
They are colored to emulate different lighting conditions. Note that the fur is also different colors in the different shots.
A darker shade of the same color isn't the same as a whole other color.
Continuity mistake: After Pumbaa kisses Simba's feet, Timon says, "Don't he's not the king," he puts his hands on the middle of Pumbaa's snout. But in the very next shot, Timon's hands are now at the top of Pumbaa's snout.
Other mistake: During "Can You Feel the Love Tonight?", Simba's reflection in the water isn't very consistent - the rocks he's standing on are much closer to the water than they appear in the reflection. (00:58:45)
Continuity mistake: In the scene where young Simba and Nala are singing, "I Just Can't Wait To Be King," and right before making faces at Zazu, Nala steps into the water with both front feet, but in the next shot, all her feet are firmly on dry ground.
Revealing mistake: In the scene where Mufasa and Simba are at the very top of Pride Rock and Mufasa is explaining the kingdom to Simba, one of the hand written sequence markers on the gel print is not removed. In the shot that zooms in on Simba just after the camera pans around them, there are two frames where the number 45 appear just to the left of Simba's tail. (00:09:15)
Continuity mistake: Before Simba and Nala tumble downhill into the elephant graveyard, Simba pounces on Nala but ends up getting pinned to the ground. At first she has her paws on his chest, but when the shot changes she holds him down by the upper arms instead. (00:17:50)
Continuity mistake: When Simba creeps up to the water's edge expecting to see Mufasa, a ledge's reflection on his right side disappears between shots, only to get replaced by tall grass. (01:05:45)
Continuity mistake: Timon faces different directions on top of Pumbaa's snout after being asked about keeping Simba. At first he looks at Simba over Pumbaa's snout, but all of a sudden he's turned around and looking right into Pumbaa's eyes between shots. (00:42:00)
Continuity mistake: During the stampede, the branch onto which Simba hangs changes shape between shots.
Continuity mistake: After reuniting with Simba, one of Nala's paws changes its place on the ground between shots. When Simba denies being the king, he begins to walk off screen to the left. Here, Nala stands several feet away from Timon. But by the next shot one of her paws is suddenly inches behind Timon instead. (00:56:40)
Other mistake: When Mufasa is teaching young Simba how to pounce, his left (our right) eye colour very briefly disappears when he starts saying "Let an old pro show you how it's done."
Continuity mistake: At the start Rafiki puts the "paint" on Simba's forehead just above his eyes. When he puts the dirt on Simba the "paint" is much higher. (00:03:20)
