Corrected entry: When Ferris calls Cameron, he is lying in bed. The phone rings and he says "I'm dying." Then he answers the phone and Ferris says "you're not dying, you just can't think of anything to do." Cameron had not answered the phone yet, so there is no way that Ferris could have heard him say that he was dying.
Corrected entry: At the end of the movie when Ferris' parents come home you see their foyer by the front door loaded with get well flowers and balloons, etc. Who accepted the deliveries if no one was home all day? Rooney wasn't around long enough to have brough ALL those flowers and gifts inside. Also, as much as he despises Ferris, I'm sure he would rather see them on the front porch to wilt. The only reason he signed for the first one was because he just happened to be standing on the front porch when the deliveryman arrived.
Corrected entry: Jeanie doesn't undo her seatbelt before she jumps out of the station wagon. And additionally in one shot of the car parked - the seatbelt is slammed in the door of the car and hanging out but when they cut back to the car seconds later, the seatbelt is gone.
Corrected entry: When Jeanie is racing to beat Ferris home, a cop chases Jeanie and eventually Jeanie pulls over. Later, Mom says that Jeanie got a speeding ticket. It is unlikely that Jeanie would have gotten home before Ferris or Dad after pulling over and getting a speeding ticket(s), yet somehow Jeanie gets home first.
Corrected entry: When there is a commotion in Rooney's office and Grace is on the phone a green binder appears on Rooney's desk. It was not there before.
Corrected entry: When Ferris rings Rooney to asks if his sister can bring any work assignments home, he's speaking with a healthy, cheerful voice. Seems weird that someone as smart as Ferris completely forgets that he is meant to be sick that day, especially when he is speaking to the Dean.
Corrected entry: At the beginning of the movie when Ferris and Cameron are taking his dad's Ferrari out to pick up Sloan there is a very old green classic car in the background of the garage. Later in the movie when they return it is missing. It isn't very likely that sometime during the day Mr. Fry returned home from work to take it out for a drive without noticing the Ferrari which he never drives is missing.
Corrected entry: In the scene where Ferris jumps into the pool to save Cameron, you see the white chair before he jumps into the water. The chair gets knocked into the water and you can see it floating from beneath the water's surface. When Ferris drags Cameron out, you can see that the chair is gone, not floating or on land.
Corrected entry: Towards the end of the movie, the Ferrari is lifted up on a jack and is running in reverse to "take off the miles." In the next scene you see the wheel, but it is spinning so that the car would be going forward, not in reverse.
Corrected entry: Near the end, there's a huge parade in downtown Chicago being held in the middle of a school/work week with no explanation about why it is in progress when parades are typically held on the weekend. Despite that, hundreds of people, who would normally be working, are there watching it with their kids who, like Ferris and his fellow truant pals, should be in school.
Corrected entry: At the end of the film Ferris introduces himself to two bikini clad woman sunbathing in their garden. The setting sun and long shadows show it is late afternoon or early evening. Ferris is wearing a heavy jacket so it is not an especially warm day, and both women are in heavy shadow! They aren't going to get much of a tan.