Continuity mistake: When the chariot with Eric and Ariel jumps over the cliff, they both disappear in the angle shot from below.
Continuity mistake: During Eric and Ursula's wedding, the carpet swaps from being plain violet colour when they walk towards the Minister, to having flowers painted on it when Vanessa transforms back into Ursula.
Continuity mistake: When Scuttle rips the seashell necklace from Vanessa's neck, the shattered pieces land at Ariel's feet, but a few seconds later they're gone.
Factual error: When Louis the chef starts to sing he mentions typical French things like "Maurice Chevalier", a french actor who became very famous as of the 1920's. Though the movie is timeless, the clothes and lifestyle (pirates, ships, horse carriages) set it long before the 20th and even the 19th century.
Answer: Yet another Disney urban legend.
Jazetopher