Continuity mistake: When Ferris is in the phone booth, he tries to get the operator but then hangs up the phone. He then scans the Town Square. The camera pans counter-clockwise and the receiver is nowhere in sight.
Visible crew/equipment: As Ferris is standing in front of the bakery, you can see the reflection of several crew members in the window. You can also see the reflection of another crew member on the glass inside the phone booth.
Continuity mistake: The clock in the booth with a broken face is shown in a distant shot, then in a close-up, where more cracks appear in it than before.
Continuity mistake: When Ferris enters the cafe and announces they have a customer, he still has the stick in his right hand. He lays the stick on the counter as he begins to climb across. As the camera pans, and then back as he gets on the counter, a menu is now covering the stick.
Other mistake: When Mike first walks into the town he sees the ringing church bell then looks to his right. The camera acting as his POV pans from left to right but since he was already looking to his right then the camera would be facing the direction he just came from.
Other mistake: When Ferris first arrives in the town the the church bell chimes seven times indicating it's 7 o'clock. Later the bells chime again but this time only four times indicating 4 o'clock. Surely he didn't walk around the empty town for 9 hours.
Suggested correction: Since the revelation of the episode is that Ferris is merely in a simulation, it stands to reason that they control how quickly time passes for him.