Okay during the part where the dad comes down the street and is playing the song "Fame" if you watch when they pan the street after the guys start fighting and you look at the taxi a dancer slips underneath the cab and then jumps up and starts dancing again.

Not only is the woman in the car Nancy Wilson, she's also Cameron Crowe's wife.

When Brad is getting fired from All-American Burger there is an "employee of the month" poster with his picture on it!

While Brad is taking food to a customer in his pirate uniform he comes across a beautiful girl in a car, it is none other than Nancy Wilson from the music group Heart.

This really isn't hidden, but Ferris has a Simple Minds poster in his bedroom. Simple Minds' "Don't You Forget About Me" is also famously featured in another John Huges film, The Breakfast Club.

In the shot with the answering machine with the supposedly grieving family, there is a U2 poster in the background.

When Mr. Rooney car pulls up to the Pizza Place/Arcade to bust Ferris, his license plate says "4FBDO" (For Ferris Bueller's Day Off), which is impossible, because in Illinois, only trucks can have plates that start with a number.

Almost all the license plates in Ferris Bueller's Day Off were named after other John Hughes movies. Ferris's mom's car says "VCATION," for "National Lampoon's Vacation." His dads reads "MMOM," for "Mr. Mom." And his sisters says "TBC," for "The Breakfast Club." On top of all that Mr. Rooney's car says "4FBDO," for Ferris Bueller's Day Off.

When they are driving to the city in the Ferrari they are actually going South which would be leaving the city. Ferris's sister's license plate says TBC, referring to John Hughes' The Breakfast Club.Did you notice how Mr. Rooney's hand changes when he's ringing the doorbell?? The first time he does the arm is covered with a sleeve, later on there is no sleeve, just a hairy arm.

When Cameron reaches down to answer the phone, it was actually John Hughes's finger that actually pushes the button.

This in not really hidden, but since it was mentioned that Ferris's sister sung Danche Shan, I would like to mention that Ed Rooney also sings it in the movie. He sings it when he is in front of Ferris's house while he is waiting for someone to answer the door

"Shoeless" Joe Jackson was a left handed batter. Ray Liotta played him right handed.

Although it's a bit of a 'chick flick', I have watched flashdance. Anyway, the dance sequences from the film involving the main character (I said I watched the film, I didn't say I liked it), mainly the quite complex ones, are performed by a professional dancer; who just happens to be a rather effeminate man. This obviously doesn't apply to the scenes where you see the face of the dancer...

Several scenes in the movie show Jennifer Beals riding a bike, and when she turns a corner, she is in a totally different part of Pittsburgh! I grew up in Pittsburgh, and you definitely can't go from one of these corners to another in a short amount of time!

When Max the robot reveals his other alien "passengers" to David, he mentions the snakelike alien in blue liquid tank is from "The PIXAR Elliptic". This was another inside joke! The PIXAR company was started in the mid-80's by former Disney FX guys, who started making full CGI shorts, and in the 90's teamed with Disney to make CGI movies like "Toy Story", "A Bug's Life", "Monsters Inc.", and "Finding Nemo".

The scene where Arial is standing between the car and the truck and jumps into the truck at the last second. When the truck is on the side of the road, she is sitting back up. The next scene she is getting up for the first time.

When Cowboy dies, in the background directly behind cowboy is a piece of burning rubble that looks like a Monolith from '2001 a Space Odyssey' (Another film by Stanley Kubrick).

In the very opening scene when the drill sargeant is introducing himself to the recruits, we see him walk from the line of troops on one side of the room to the other. When he comes back to the side where he started, the troops are in a completely different order in line. In fact, Vincent D'Onofrio (Private 'Pyle')is originally on the opposite side. When the Sarge runs back to the line of troops he started with, 'Pyle' is there also. Thus begin the classic, in-your-face tongue lashings from the Sarge.