Anachronisms: While the story is set in 1886, the Victrola plays "The Stars and Stripes Forever", by Sousa, which wasn't composed until 1896.
Continuity: In the opening titles, Fievel's name is spelled "Feivel".
Errors in geography: Fievel and his family board their ship in Hamburg, in northern Germany, but the band welcoming the passengers is a Bavarian traditional band that would never play there.
Anachronisms: We see Fievel outside of a mouse school with little mice reciting the Pledge of Allegiance. This wasn't written until 1892, over six-and-a-half years after the 1886 setting of the story. In addition, the phrase "to the flag of the United States of America" is used; the original version of the Pledge featured instead "to my flag", and was not changed until 1923, 37 years after the setting of the story.
Continuity: When Tony is reunited with Fievel, he steals a piece of cheese from a mouse trap and throws it up in the air. The cheese disappears before it leaves the top of the frame.
Continuity: When Fievel falls off an elevated track and lands on a pile of soot, he burrows his way out, leaving a trail. When he makes his way out, the last part of the trail disappears.
Continuity: When Warren T. Rat sees Fievel through his mirror, the reflection is not reversed (note the position of the gold teeth).
Continuity: When Tony first sees Bridget, and runs to the hole in the wall, his hat lands on Fievel's head. Although Fievel is still wearing it when Tony falls off the awning, it has disappeared by the time Fievel is trying to pull Tony away from Bridget. Although Tony is hatless in the Tammany Hall scenes, he is suddenly wearing it again when his alarm clock goes off, after the scene at the pier.
Continuity: From Bridget's first appearance, up until after she and Tony kiss, she has a parasol. It is last seen at her side when she sits down with Tony, right before Fievel tells the crowd that there are no cats in America. When Tony and Bridget emerge from the wreckage, it has disappeared; when Bridget leaves for Tammany Hall with Tony and Fievel, she leaves without it.
Continuity: When Tony pulls Bridget from the wreckage at the market, she has a white petticoat under her dress. When she lifts her skirt up while searching for Fievel during the fire, only the underside of her outer dress is seen.
Anachronisms: One wide shot of New York features the Verrazano Narrows Bridge, which was not built until 1964.
Factual errors: At the end when the Mousekewitzes look back at the Statue of Liberty we see the front of the statue, and behind it we see Manhattan and Brooklyn. That would have the statue facing south, but the Statue of Liberty points east so if they we're looking at the front of the statue they should be looking at New Jersey.
Factual errors: A mouse on the boat to America tells a story involving a calico cat ("tortoiseshell"). Several times, he refers to the cat as "he" or "him". Unless suffering from an extremely rare genetic defect, all calico cats are female.
Continuity: The number of petals on the flower in Bridget's hair changes from scene to scene.
Continuity: At the end of the song "Never Say Never", Henri and Fievel are standing by a hole in the unfinished Statue of Liberty, facing the tablet on her left hand. From inside, the top of the tablet appears to be some distance below the hole, but as Fievel is flown to immigration, the hole is seen level to the bottom half of the tablet.
Continuity: When Fievel climbs down into the sewer he leaves his hat on the grate. In the following few shots he is still without it. A bit later he is still walking, but clutching the hat in his hand.
Continuity: During the chase inside the cat's lair, Fievel's hat, which is tucked in his belt at the back, disappears in some shots.
Plot holes: The main plot of the story revolves around Fievel being separated from his family and then the family trying to reconnect. At the start of the film there are five family members, Mamma and Pappa, Fievel his sister and the baby. Pappa even makes a sad miscalculation when coming through Ellis Island saying he has five, then corrects and says four family members. Well, after the first half of the film the baby completely disappears from the movie and at the end of the film there are only four family members.
Anachronisms: Although Edison invented the phonograph in 1877, it did not become available for home use until 1896 (10 years after this story took place). In fact the Edison Phonograph Company was not formed until 1887.
Continuity: In the establishing shot of the water tower where Bridget leaves Fievel, the moon is high in the sky. A couple of shots later, as Fievel starts singing "Somewhere Out There", the moon is just rising over the horizon.
Continuity: During the scene in which the cats are coerced into the ocean by the mice's secret weapon, and consequently lifted by anchor into the boat to Hong Kong, Tiger can be clearly seen as one of the cats on the anchor. Tiger obviously appears again later in the movie to help the family find Fievel.