When Cruella gets thrown in the air in the barn, the glass breaks before she hits it.
When Dipstick is falling down the rain gutter, he is not wearing his collar.
The amount of ash that Cruella drops off her cigarette.
The amount of molasses on Cruella's face changes from the time she gives her speech to the animals to when she's thrown out of the barn and into the pig pen and when she gets arrested.
During the movie, Anita never has a baby bump. Both she and Perdy find they are pregnant at the same time. Dogs are pregnant for about two months. The puppies we see during the majority of the film would be about three months old. This means that by the time the puppies are stolen, Anita would be at least five months pregnant and have a noticeable bump.
When the dogs are watching Homeward Bound: The Incredible Journey (1993) on the television, scenes from the movie are played out of order.
It should have been impossible for Anita to carry bricks in her bag as bricks due to their size and weight would really rip open her bag and it would also make it impossible to put several bricks in a bag the size of Anita's.
Raccoons and skunks are not native to Britain. However, there are some feral populations there, descending from animals imported for fur, consistent with the movie's theme.
Just before Jewel receives her collar, it can be clearly seen that she is actually a male puppy.
After Roger and Anita have met in the park we can see Pongo has been neutered whilst waiting to cross the path.
In addition to the American style of dates month/day/full year used on Cruella's check to Anita, the check is dated October 31,1976 (without the st after the number) This movie is set in clearly set in 1996, there should be no reason why it would be dated with 1976. The chosen date of Halloween or the year 1976 has no particular connection to either adaptation, the original book or anything related to them.
Tube providing fluid clearly visible when Whizzer is urinating on floor.
When Cruella is thrown by the horse through the window, there is a harness holding her.
When Perdy is taken to be checked by a vet because of her pregnancy, the window says "Veterinarian". This is the North American term - in the United Kingdom vets are called "veterinary surgeons".
When Cruella attempts to hand over the cheque to Anita and Roger, it can be clearly seen dated in the American format, mm/dd/yy. Also the bank sort code on the top right doesn't correspond to the second set of figures at the bottom, which is the case with UK cheques.
The woodpecker in the film does not belong to a species native to the British Isles.
Roger and Anita's house is located in South Kensington, as can be seen on the street sign outside their house several times. This is north of the River Thames. In one of the later scenes the view from their rear window shows the River Thames, Tower Bridge, and Big Ben as seen from the south bank.
Alongside the other already documented American anachronisms that jar with a British audience (racoons, skunks, US date on a cheque, "veterinarian" vs "veterinary surgeon"), on learning that she could be pregnant Anita immediately visits an Obstetrician. In the UK, the first port of call for a first pregnancy would to be her General Practitioner (GP). If there were complications, only then they would refer her to an Obstetrician.
After dog napping the puppies, Horace and Jasper go to De Vil mansion for further instructions. After Kipper the Airedale terrier finds this out, the message back to Pongo and Perdy takes at least 24 hours, yet the two villains are seen sleeping at the manor as though they arrived there a few hours ago.
Anita somehow did not know she was pregnant until Nanny told her. If Anita had missed a part of her menstrual cycle, then she should have suspected she was at least expecting.
In the 1961 animated version Pongo wears a red collar and Perdy wears a blue collar. In this version Pongo wears the blue collar and Perdy wears the red collar.
When Jasper and Horace are waiting for Roger and Anita to leave to take Pongo and Perdy walking Horace is seen in the driver's seat which meant he drove there although he never drives. It's Jasper who always drives.
After the Priest marries Roger and Anita and Roger is about to kiss Anita the Alter Boys standing behind the Priest give a shocked and scared look.