Continuity mistake: As Buddy walks out into the street at the start of the movie when the cat is playing dead, you can see several parked cars on the street behind him. When the van backs up to 'catnap' buddy, there are no parked cars. Then as the van drives off again, there is a different bunch of parked cars in the street. (00:03:54)
Continuity mistake: It is clear throughout the movie that the dog that plays the character "Lou" changes from a male to a female. You can tell in different scenes when Lou is standing up, it's a male dog, and when Lou is laying on his back, belly facing up, it is a female dog.
Continuity mistake: When the cats drive into the factory the same hubcap falls more than once from the car. (00:50:55)
Continuity mistake: When Mr. Tinkles starts the room on fire at the end, parts of the room that are nowhere near the fire, are on fire.
Continuity mistake: At the beginning of the movie, a woman takes a pie out of the oven, leaving the oven open, and then gets hit by the cat flying through the window. As she falls back, the oven has magically shut. (00:02:40)
Continuity mistake: At the very beginning of the movie, as the 4x4 draws up outside the house, a woman (Carolyn) jogs past. However, in the next shot, the same woman has now moved back along the road, and jogs past the 4x4 again. (00:01:10)
Continuity mistake: When the kid is home after the soccer tryouts and he does not get in he kicks his soccer ball and misses the goal. Seconds later he kicks another ball, despite not having one there. (00:33:15)
Factual error: The "Russian Blue" isn't a Russian Blue at all. Russian Blues have pointed faces and green eyes. The flat faced, orange eyed kitten is a British Shorthair AKA British Blue. (00:39:35)
Other mistake: When Butch says "Welcome to HQ", his mouth isn't being animated.
Deliberate mistake: Whenever we see the computer generated Lou, he never has genitals.
Continuity mistake: When the cats are having a meeting and the maid comes in, she picks up Mr Tinkles. She goes to put him on her left shoulder. The camera quickly cuts and he is on her right shoulder. When the camera changes angles again the cat is on her left shoulder. (00:19:35)
Deliberate mistake: When the Russian cat sets the bomb on the big metal door, it is set for one minute. Yet this one minute seems to take three minutes to count down. I know it would be boring if it really was one minute, but why didn't they just make it so the cat set it to three minutes? (00:45:00 - 00:50:00)
Continuity mistake: When the boy is playing with Lou he rolls around in the mud, seconds later there is no mud on his knees or his bottom.
Continuity mistake: When the video of Mr. Tinkles threatening to 'put the Brody family to sleep' is seen in the background at HQ, it is noticeably different to when the dogs saw it first time. This is easier to verify when Mr. Tinkles says, 'they will be put to sleep.'
Factual error: When the Russian Blue is in Luke's house, there is a shot where Butch is tangled up in the telephone wire but it should actually be mirrored since it was the reflection in the cat's eyes.
Continuity mistake: When Lou walks knocks the door into the burning room where the kid and his parents are, you can see that Lou has a circled chain. However, in the next few shots it appears as a bone shaped chain and then it changes back to the circled chain. (01:14:40)
Continuity mistake: When Buddy the Bloodhound is chasing the ginger cat through the womens' house at the beginning, you see a shot of the cat from Buddy's point of view which shows the cat sitting down. Yet in the next shot that zooms in on the cat, it is standing up. (00:03:10)
Continuity mistake: In the scene in the flocking factory when Jeff Goldblum's character is being confronted by the cat leader (Mr. Tinkles) another cat (Calico) is on Goldblum's shoulder. When the shot changes to an angle behind Goldblum, Calico disappears only to immediately reappear when the shot changes back to the angle facing Goldblum.