When Paolo sets out to brush Mia's hair, he orders his assistant "Helga" to hand him the brush in make-believe German. He says, "Brüste, Helga," which translates as, "Breasts, Helga." The correct word for "brush" in German is "Bürste".
When Queen Clarice and Mia are talking to the police after Mia hits the trolley car, the queen tries to claim diplomatic immunity as a way to get out of the ticket for the accident, which the officer promptly denies, as Mia is not subject to immunity. However, traffic tickets have never been included in offenses excused for diplomatic immunity. Thus, even if immunity had applied to Mia, she still would have gotten a ticket.
At their second meeting, Clarisse tells Mia to wear "stockings, not tights" on her next visit. However, the garment that Mia is putting on in the back seat of the limousine, en route to the consulate the next day, is a pair of tights, not a pair of stockings, as the queen specified.
The Genovian motto written in Latin "Totus Corpus Laborat" has a grammatical error in it. The motto should actually be "Totum Corpus Laborat". Totus is a masculine form of the adjective, but the noun corpus is neuter.
Mia misquotes Shakespeare's Juliet as saying, "What's in a name? That which we call a rose by any other word would smell as sweet..." Juliet's line is, "What's in a name? That which we call a rose by any other name would smell as sweet".
Before Mia slides down the firepole during the opening scene she is wearing glasses. When she gets to the bottom of the pole she isn't wearing them then when she walks across the room to leave she has them on again.
When Josh is hit with the softball, the ball bounces out of sight. In several consecutive shots, the ball is nowhere around him. However, when another boy yells at him to "pick it up", the ball suddenly appears next to him, and he throws it home.
When we first see Mia after the makeover, she is wearing make-up: eye shadow and lip gloss. But when she turns to look at herself in the mirror, eye shadow has disappeared and her lip gloss has become lighter.
The cucumber slices that Paolo puts over Mia's eyes change from having part of their skin peeled off to having a continuous peel around their circumferences. As her make-over occurs within a relatively short period of time, there seems to be no reason for the slices to be changed.
When Mia is walking by the group of cheerleaders tormenting her about her public speaking anxiety (..."bullimic convention?"), Lana sits down, then sits down a second time without ever getting up in between.
When Mia is driving the Mustang up hills with her grandmother, it is implied that it is a manual because it keeps drifting backwards on hills (it even drifts all the way down a hill and hits a bus). Also there is a close-up shot of her putting both feet on the brake pedal. Later in the movie when she's driving to the ball in the rain, the car stalls and she lays down on the front passenger seat. You can clearly see the gear shifter and it is an automatic. Therefore it wouldn't drift backwards on hills.
Helen tells Mia that they (the Queen, Mia's dad and Helen) were planning on telling Mia about her heritage when she turned 18. However the letter from Mia's dad was for her 16th birthday and it has the royal insignia on the letter head. Wouldn't that give it away?
When we first see Michael at the auto shop he's practicing with his band. They show two girls watching the band. One of the girls says, "He fixes cars, he plays guitar... and he can sing -He is so hot! -He is wicked sweet. ". While she is saying this the camera is set on Michael, who is playing the keyboard, not the guitar which indicates she is not talking about Michael but the guitar player who can be seen talking to the girls later in the scene.
When Mia takes the trash out in the opening sequence, the neighbor's mailbox has his last name printed on it. When Queen Clarisse arrives to talk to Mia after she has run away from the consulate, Mr. Robutusen is getting his mail and there is no name on the mailbox.