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.
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?
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.