Continuity mistake: When Tiger and Fievel are doing their musical piece, Tiger wipes off the mirror and they appear the same size. When he lays out in front of the mirror, singing the line "We'll be there to pick each other off the floor", he places his head next to the cage bottom, still laying on the floor between them. In the mirror, however, that cage bottom is not reflected at all. (00:57:30)
Continuity mistake: When Fievel is first heading down the storm drain, as he believes his father is playing his violin, he leaves his hat on the surface, but a few seconds later he is seen holding the hat as he gets closer to the gang of cats.
Continuity mistake: Watch the small bed inside the water tower. Soon after the song 'Somewhere Out There', a small piece of cloth appears from nowhere on it. (00:41:10 - 00:43:15)
Continuity mistake: When Warren takes Fievel to his henchman Moe who is a rat, he is the same size as Moe. He is even able to go through the very small hole in the wall into the room. Later in the movie, Warren is now seen being the same size as a cat.
Continuity mistake: Just before Gussie leaves Mickey O'Hare's wake, Fievel can be seen in the background behind Honest John eating a large piece of cheese from a nearby teacup. However in the next shot he's standing in a completely different location and no longer has any cheese in his hands. (00:40:05)
Continuity mistake: When Warren T. Rat is playing the violin off-key, he hits a bad note and blames his fake nose for getting in the way. With the bow still in hand, Warren grabs his nose and proceeds to twist it off. But the bow vanishes in the next shot as his nose snaps free. (00:50:50)
Continuity mistake: At Mouse Garden headquarters outside of the Commission of Immigration, several vendors are trying to sell things to a crowd. Below a top hat is a sign which distinctly reads 'Mouse Garden'. But fast forward to the one offering a used ticket to Chicago right near the headquarter entrance and you'll see how it now says 'Immigration Mouse Garden' instead. (00:24:35)
Continuity mistake: When Fievel discovers that Warren T. Rat is actually a cat in disguise, the hat tucked into his black belt disappears between shots. (00:51:20)
Continuity mistake: When Fievel is running after Tony in the back alley, he gets stuck in a sewer grate hole and hears what he thinks is Papa's violin coming from down below. Throughout the scene at some points, Fievel instantly appears in different grate holes. (00:48:20)
Continuity mistake: After the Giant Mouse of Minsk lands in the ocean, a vacant pier can be seen from an underwater perspective. But once the angle changes seconds later, all of the mice are suddenly looking down below at the wreckage. Additionally, two ropes appear from nowhere hanging over the pier's edge. (01:04:30)
Continuity mistake: After Tony whistles at Fievel from atop the Hester Street lamppost, Fievel's blue hat can be seen lying in a puddle. But between shots the hat moves itself onto dry ground. (00:33:25)
Continuity mistake: After Fievel gets captured by Warren T. Rat, he's ordered to work alongside numerous other mice in a tailor shop. In the following scene where everybody's asleep, Fievel jumps from his bed and walks over to the nearest window - making a reference to Rapunzel's hair and how well it would work to escape with. All of a sudden, two long white sheets conveniently appear on the floor behind him out of nowhere, from which he makes a long rope to rappel down the side of the building (not unlike Rapunzel's hair). (00:28:50)
Continuity mistake: During Mickey O'Hare's wake, Honest John's shot glass refills itself between shots, at the point where he asks Gussie Mausheimer, "What's a wawwy?" (00:39:40)
Continuity mistake: When the secret weapon is released from Professor Digitalus' Museum, it demolishes the door and scares every cat onto the Star of Hong Kong's anchor. Just a few minutes later, Fievel can be seen passed out on an eyehook in the vacant museum. That's where a flame ignites a trail of kerosene, but when it soon becomes a full-blown fire, the door is once again intact (locks, chains and all) as though nothing happened. (01:03:10 - 01:05:55)
Continuity mistake: During "A Duo", Tiger picks up Fievel's cage and places it on a nearby step. Between shots, the cage tray decreases in size significantly (judging by the overhang). (00:56:35)
Continuity mistake: When Papa's story is interrupted by the Cossack cats, some of the tableware gets knocked over and broken. But seconds later, in the shot where Fievel runs outdoors with a pot and spoon, all of the broken items reappear intact. (00:05:45 - 00:06:25)
Continuity mistake: After Fievel tumbles from the railroad tracks, he can hear what sounds like Papa's violin coming from a building nearby. While he's running towards the street, his hat turns itself around between shots. (00:31:30)
Continuity mistake: When Fievel emerges from beneath a tea kettle cover and collapses onto the snow, Mama walks over and scolds him. A moment later, Fievel's feet are suddenly missing their pads. (00:07:20)
Continuity mistake: When Fievel sits on the Statue of Liberty's torch, his right hand repositions itself between frames. First it's between his feet, then the outside of his left leg. (00:20:40)
Continuity mistake: During the storm, Fievel crawls to the edge of the step he's on and watches two fish flop around below deck. Keep an eye on his blue hat. At first it's in his left hand, but between shots the hat somehow jumps below the step he's on - from which he pulls it out with his right hand and places it back on his head. (00:16:10)
Answer: Warren T. grabbed Tiger and told him he was fired.Tiger did eventually leave some time after that though.