Right before The Cat comes in with the D.I.R.T. machine, Sally and Conrad are standing next to each other holding hands as the door begins to open. When the door opens, they are no longer holding hands and standing a few feet apart.
As the children are waiting for the door to open as their mother returns they reach out and hold hands with each other. But when the door opens to reveal the Cat the children area standing apart and not holding hands.
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.
While in the car, Cat gives both the kids their own steering wheels. When he pulls out his own, its a chain wheel, but when the camera switches its a normal steering wheel. Later in another shot, it's a chain again.
When Quinn enters the house for the first time and sets his briefcase on the table, he places his glasses on top of it. In the next scene, where he tells Conrad about military school, the glasses are missing, and in the following shot they reappear on the briefcase again.
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 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.
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.
When the Cat gets hit in the crotch, it immediately cuts to him in the wintertime with "Easy Like Sunday Morning" playing. However, if you look in the upper right corner, you can see the green grass and a concrete sidewalk.
When Conrad slides out the door, Mom's car is parked against the flow of traffic. From earlier scenes, we know that the street is a two way street. By law, drivers must park their cars in the direction of the traffic flow on the side of the street where they park.