Continuity mistake: When the butler takes the mother and kittens to be abandoned in the countryside he is on a motorcycle and sidecar combination. During the trip the sidecar changes from one side of the bike to the other and back again. Also, when the sidecar separates from the motorcycle when the dogs are chasing Edgar, the wheel on the sidecar switches sides regularly as well.
Revealing mistake: When Madame gets off the carriage, Frou-Frou winnies to get her attention. Madame then proceeds to feed her. Frou-Frou eats from her hand. However, if you look closely at Madame's hand, it is empty. (00:03:05)
Continuity mistake: When Edgar is escorting George up the stairs, George's cane gets caught in Edgar's legs. However, in the very next shot, the cane is held high up in the air by George, when it should be still caught up in Edgar's legs. (00:04:56)
Continuity mistake: When the mouse gets in the light in the back of the motor cycle, there are little bits of glass sticking in from where a full glass cover had once been. But when they show the mouse bumping up and down there is no glass.
Continuity mistake: When O'Malley arrives with his musical number, as he strides around Duchess before he 'curls' his fingers, her collar changes color for a split second quite visibly during the same shot.
Other mistake: When Edgar goes to retrieve his hat and umbrella, he uses a fishing pole to snag the hat from Napoleon's head. You see him reeling in the line when it should be reeling out (counter-clockwise vs. clockwise)-the next shot shows the line going down. This happens twice.
Continuity mistake: When O'Malley jumps on to the milk van, it screeches to a halt. The milkman gets out of the van to manually crank start the van. However, in the previous shot, there is a clear view of the front of the van, and there is no crank shaft present.
Continuity mistake: When the male kitten plays the piano for his singing sister the painting kitten starts to join him. His paws are covered in paint. During a brief scene change you can see that the colour of the paint on his left paw has changed. Also he only has two colours of paint on him, but minutes later the keyboard is covered in all colours of the rainbow.
Continuity mistake: When the cats get catnapped, Berlios's ribbon becomes undone as shown by the uneven length of the two ends. When he walks out of the stream, his ribbon is miraculously neat and tidy.
Factual error: When Edgar the Butler directs the Old Solicitor upstairs they have a bit of a struggle with the steps. Before this you saw the Solicitor arriving in his car and this gave you an impression how high the first floor of the building of the Old Spinster was. Judging by the amount of steps on the stairs the pair would have ended up on the roof.
Continuity mistake: Edgar gets the seat bitten out of his trousers at least three times when being pursued by the dogs - it miraculously repairs itself.
Continuity mistake: When the butler gets placed into the trunk to Timbuktu, from the time he leaves the barn to the moment he gets lifted on the mail truck, a lock magically appears on the trunk.
Continuity mistake: When the lawyer is getting out of his car, he removes his driving gloves and holds them in his hand together with his briefcase. However, when he gets out of the car, the gloves are missing. (00:04:09)
Continuity mistake: The kittens fight and a candle falls on the floor. The candle is part of the moving parts against the fixed background (decor). In the following shot the candle has become part of the background and thus changes colour and shape. In the next shot when the cats walk away from the area where the candle fell, the candle has disappeared.
Continuity mistake: The painting kitten (in the beginning of the film) steps on a tube of blue paint and squirts a bit that ends up on the floor. Minutes later the colour of the blob on the floor has changed to red and a few moments later the paintblob on the floor has vanished. During the 'paint' scene several tubes near the palette also change colour and position.
Continuity mistake: When Edgar takes the cats to the countryside he looses his shoes in the struggle with the dogs. When he finally leaves the scene his shoes are back again.
Continuity mistake: Marie falls off the viaduct into the river but doesn't get washed along by the current at all (until they spot her and start the rescue that is).
Other mistake: When the three kittens are playing train on the train bridge, Berlioz is standing in front, then Toulouse, then Marie. After Berlioz says, "Marie's the caboose," look at Marie's reaction, and Berlioz is painted in front of her instead of Toulouse.
Factual error: At the very beginning when the family are in the cart being pulled by Frou-Frou, the way Frou-Frou is trotting is completely wrong compared to how a real horse trots. When she is moving it is front and back right, and then front and back left. It should actually be front right and back left and vice-versa.
Continuity mistake: When Georges enters Madame's room, the kittens' eyes can be seen all black, especially Toulouse's when the lawyer is dancing. A few scenes later, the kittens' eyes are back to normal.
Chosen answer: It is the style of the artwork. Similarly, it is not a mistake that each individual hair is not drawn, the eyes are not really proportional to the head, etc.
Myridon