The placement of the mannequins inside Resnick's changes.
In the police station, Ferris' right hand touches a jail cell bar, causing the entire cell wall to wobble flimsily.
When Ferris pokes his head in the doorway of the bakery, several moving crew members heads can be seen reflected in the front glass window- at about the level where the pies are displayed.
When Ferris is in the phone booth and hangs up the phone, a man with dark hair and glasses can be seen in the reflection of the door glass.
Just after Ferris (Earl Holliman) jumps over the counter of the diner, the heavy shadow of the camera can be seen to encompass the napkin holder on the counter.
When Mike approaches the projector in the theater, on the right side you can see the arm of the crew member holding the light to shine in his eyes as they aim it wherever his head moves.