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: During "A Duo," Fievel is standing on a cage tray which Tiger slides next to a dirty floor mirror. Once Tiger begins singing the chorus, the tray disappears - only to reappear in its original location once Fievel wipes the mirror clean in the next shot. (00:57:05)
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: Throughout the entire scene involving Fievel being locked in a cage and singing "A Duo" along with Tiger, his blue hat is nowhere to be found. But after the floor mirror's glass shatters, he and Tiger are locked in a handshake and, all of a sudden, the hat is now tucked under his belt. (00:58:30)
Continuity mistake: When Fievel is being pursued by a gang of cats, he runs into the museum and tries waking everybody up. At one point his left leg slips itself into his pants between shots. (00:59:35)
Continuity mistake: After Gussie knocks a growling cat in the head from atop the museum marquee, several mice suddenly appear to her right in between shots - tossing various objects at the other cats below. (00:59:55)
Continuity mistake: When Warren T. Rat is near the museum's entrance trying to negotiate with Gussie, he's wearing his purple nightcap and a rat disguise. But Tony's not convinced he's really a rat, so he sets out to expose Warren T. by firing his slingshot. In the following shot part of Warren T.'s disguise falls off as planned, but he's now holding the nightcap instead of wearing it. After replacing the nightcap he tries to explain his way out of the situation, but once again in the very next shot where Tony takes aim to fire a second time, he's suddenly shown holding the nightcap. (01:00:30)
Continuity mistake: When Warren T. Rat gets exposed by the mice and sets fire to Professor Digitalus' Museum, the word 'professor' is missing from the marquee at some points. (01:01:00 - 01:02:30)
Continuity mistake: While Honest John is pushing both hands against the secret weapon to keep it from escaping, a clock strikes 6:00 A.M. At this point he raises his left hand and shouts, "Release the secret weapon." But when the shot changes, he's suddenly got both hands in place on the weapon once again. (01:02:00)
Continuity mistake: After the secret weapon breaks free from Professor Digitalus' Museum, some missing pieces of wood on the door frame reattach themselves. (01:03:10)
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: When the Giant Mouse of Minsk is racing towards the other cats huddled at end of the pier, Warren T. Rat is briefly missing his nightcap in one shot. (01:04:20)
Continuity mistake: When the Giant Mouse of Minsk dives from the pier into the ocean, its head gets submerged immediately. But from the next angle beneath the surface, its head gets submerged a second time. (01:04:25)
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: Throughout the orphan alley scene, from the point where Fievel gets taunted by a gang of bullies until he hears Papa's violin in the distance, the slanted window in the background is broken in different places from one shot to the other. At one point is has no visible breaks anywhere at all. (01:08:30)
Continuity mistake: As Fievel is sleeping in the hay beneath a broken window at Orphan Alley, three bullies approach and start taunting him. In the next shot, Fievel is suddenly wrapped in a blanket, which is quickly pulled out from underneath him by the first bully. (01:08:30)
Continuity mistake: After being bullied and tossed into a puddle, Fievel convinces himself that he'll never be able to find his family. Between shots, his arms cross themselves in a different manner. (01:09:35)
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.
Factual error: When Fievel is being dressed by the pigeon there are two American flags in the background. The flags have too many stars for the mid 1880s, when the movie is set.
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.
Answer: Warren T. grabbed Tiger and told him he was fired.Tiger did eventually leave some time after that though.