Goofs

When the lock is removed the dog's collar, Conrad is shown putting it into his left pocket. When locking the red box up again, the lock is being taken out of his right pocket.

When Cooking Cat is filling the Kupkake-Inator with the purple liquid, it's very messy and all over the tray. However, when the tray closes, the purple liquid is neatly in each hole.

When the real cat piñata is thrown to Conrad and Sally, it is sealed. However, after the Cat is hit with bats, the piñata is open, and after the Cat is hit in the crotch with a baseball bat by one kid, Conrad throws candy so the kids won't hit the Cat anymore.

After the crash in the automobile, one of Sally's pigtails falls down. A short while later, the pig tail is fixed and back where it's supposed to be.

The clean couch in the living room has pillows that disappear and re-appear between shots.

The Cat's certificate claims he has been both neutered and spayed. This is not possible, as spaying is for female animals, and the Cat is male.

On Sally's to-do list includes "create tomorrow's to-do list". This isn't possible, as if she has to make tomorrow's to-do list then she would have to create that to-do list the day before, which she isn't because she's doing it today. Furthermore, since creating tomorrow's to-do list is part of tomorrow's to-do list, so on and so forth, it wouldn't be possible to create tomorrow's to-do list since she would be creating it today.

Nevins the dog is shown eating a plate full of chocolates and figs in one scene. In real life, a dog would get very sick if it ate such things.

When Joan is driving away in her car, you can see that the wheels are fake and not moving.

Obvious stunt performers when Conrad, Sally, and the Cat slide down the pole into the club (different clothes and hair).

When one of the Things rides a bicycle down the staircase, you can see a string or cable trailing behind him.

While the Cat plays his keyboard, plastic sounds can still be heard, due to the fact that it wasn't a real keyboard.

When Larry takes out his false top teeth, you can still see teeth on top immediately afterwards.

After the Cat has been hit in the crotch, the party children have changed positions. They are gathered in the close up shots, but have spread out in the wide shot.

When we see Quinn returning to his house, is is about 30 feet away from the right side of the children's house. However, when the storm is approaching, we are looking at the right side of the children's house from about 200 feet away. From 200 feet away, Quinn's house would be blocking our view of the children's house.

At about 10:30am we see the babysitter is watching a "live" broadcast of an incident that happened during a Government meeting in Taiwan. When it is 10:30 am in Los Angeles, it would be 12:30am at night in Taiwan.

When Lawrence sees the Cat in disguise, he doesn't sneeze. However, it is revealed in an earlier encounter and a later encounter that he is allergic to cats, because he sneezed when he was exposed to the cat at those times. His senses would've still caused him to sneeze even when he was unaware that it was the cat.

In the original Cat in the Hat, after the children and cat had fun, the house was cluttered and there were stains all over the place. The clean machine cleaned and straightened everything up before mom got home. In this movie the house was destroyed beyond repair. This amount of destruction was beyond the capability of the clean machine. The house would need to be torn down if it did not fall down on it's own.

When the Cat is putting his "clean up machine" back in its box, purple blobs can still be seen on the door frame.

Throughout the film, the Cat refers to himself as a "six-foot tall, talking cat". However, according to his spayed and neutered papers, he is only five-foot eight.

When showing the contract, the Cat pulls out his "spay and neuter" receipt. But when hit between the legs with a baseball bat, he reacts like a male who hasn't been neutered.