As Ariel and Eric swim toward each other right before the enormous Ursula rises above the sea they exchange dialogue: "Eric, you've got to get away from here," "No, I won't leave you," but their lips never move.
Towards the end of "Part of Your World" Ariel sang the words "Wish I could be" in the shot where Flounder felt sad and three shots later she sinks, but the words don't match her mouth movement. [In the 2013 Blu-ray only]
When Ursula is explaining the bargain to Ariel, she says that she will make Ariel a potion to turn her into a human. However, neither she nor Ariel drink any sort of potion; once she has Ariel's voice as payment, Ursula simply waves her arms and makes the transformation happen.
During the song "Les Poissons", Chef Louis sings "Then I pull out their bones" and he pulls out the fishes bones and the tail fins with them. Later on in the song he sings "Then you rub some salt in 'cause that makes it taste nice" as he rubs the salt on a fish tail with the tail fins still attached, although he already pulled the tail fins out.
After Sebastian discovers Ariel's treasure cove and gets tangled up in her collection of human objects, he gets a thimble stuck on his claws. The thimble subsequently disappears and reappears between shots.
While in the castle of Prince Eric, Ariel lies down on a bed for the first time. Cut to Sebastian talking. Cut back to Ariel asleep on top of the covers. Next, Sebastian jumps on the bed, and Ariel is shown asleep under the covers.
When Eric is telling Grimsby that he wants to marry Vanessa, her hair is brown. When Vanessa is singing to herself in her cabin before the wedding and climbs onto the dresser, her hair turns black. Then at the wedding, it is brown again.
When Eric and Ariel are reunited and she got her voice back on the ship, they are about to kiss but the sundown turns her into a mermaid again before they do. Ursula crawls towards them, catches Ariel, says "So long, loverboy" and jumps into the water. When they are seen in the next shot Ariel's blue dress is suddenly gone.
When Ursula is on the boat right before her wedding to Eric she steps on the makeup table while she talks to herself in the mirror. In doing so she cracks a round crystal ball with her foot. But in the previous scene there was no such ball on the table.
The eels Flotsam and Jetsam each have one yellow eye; one has it on the right side, the other on the left. When they are talking to Ariel and the camera cuts to the close-up of them saying "Together forever," the eyes have switched places.
When Ursula is talking to Ariel for the first time, she sits down at her mirror to apply some makeup - when she looks at Ariel, she has on lipstick, but in the next shot, she has none and is applying it from a clam.
When Sebastian is trying to escape from Louis the chef, he runs under a shelf of glassware, pots, and bowls. When we see Louis running towards the shelf, he is holding a butcher knife in his right hand. Then when we his reflection in one of the bowls in front of him, the butcher knife is reflected in the wrong hand (his left hand).
When Grimsby is talking to Eric at the dining table about taking Ariel out for a day on the town, there are plates in front of all of them. But when Carlotta brings the food they have no plates in front of them.
When Vanessa is singing while getting dressed for the wedding, she throws a spike to the mirror and the mirror bends. On the shot right before she steps on the bottle, the mirror is still, and on the next shot it is bent again and she is putting it still while revealing Ursula's face on the reflection.
When Ursula is human and is singing in her chamber, she steps on the vanity where there was one purple jar to the right of the green box, but when she steps up, she smashes a new purple one that appears. When the shot zooms out, the smashed jar is now the only jar and is to the left of the green box.
After Ariel becomes human the first time, Scuttle dresses her in a piece of sail cloth from the shipwreck. Moments later, Sebastian crawls into a pocket in the makeshift dress when there's no reason for a pocket to be sewn in a sail.
When the animals are sabotaging Eric's wedding to Vanessa, Scuttle tries to pull her seashell necklace away from her. The significance of the necklace should not be evident to him, as he wasn't there to see Ursula seal Ariel's voice inside it.
Ariel signs Ursula's contract, with her name, showing that she knows how to write. However, when voiceless, she does not use this skill to write important information to Eric or anyone else who could help her.
At the end of the "Kiss the Girl" scene, Ariel is slowly turning her head to the left to face Eric. During the motion between the 3/4 view of her face and the full side view, some animation frames are apparently missing and consequently the scene of Ariel moving her head is not smooth at all.
When the Chef goes to poke Sebastian with the two-prong fork, the prongs trap Sebastian in between them and stick into the table. The holes that were supposed to be made by the fork were already there.
Just as Scuttle starts leading the birds and sea creatures on the wedding crash, the guests, Eric, Vanessa, and the minister are not visible in the overhead shot as Scuttle and the birds begin diving toward them.
During a carriage ride, Ariel makes the carriage jump a small ravine. When it hits the other side, it stops briefly, and then begins to move. As it does, the wheels do not move at all, but remain motionless.
During the final battle scene, where Ursula is about to strike Ariel with the trident, Eric steers the shipwreck into Ursula. The shot just before the ship pokes her, she is facing the wrong way (Ursula is facing Eric's direction when she should be facing Ariel).
When King Triton discovers Ariel's treasure cave, he destroys the statue of Eric. While it is breaking apart, a close up of the face shows cracks crawling across the entire face. However, later, when Flotsam and Jetsam are in the cave, they flick the face - now completely intact - to Ariel.
When Triton remarks that the only problem that remains is how much he will miss Ariel, Sebastian looks up at him surprised. However, when he points his trident to Ariel to trade her fins for legs, Sebastian has disappeared. When Ariel sees she has been given legs and smiles broadly to her father, he is back.
Throughout the part of the movie when Ariel has legs and is on land, Sebastian, Flounder and Scuttle all speak of how Ariel will regain her voice when Prince Eric has fallen in love with her and kissed her. However, when Ursula details the terms of the contract, it is never mentioned that Ariel's voice will be returned. If it was, then Ursula would have received no payment for giving Ariel legs.