Continuity mistake: At the beginning of the movie, Ryan's hair is short. In the scene where he, Anna and Tess are talking about why Anna was riding on the back of Jake's motorcycle, his hair is several inches longer. At the wedding rehearsal his hair is short again, the same length it was at the beginning of the film.
Continuity mistake: When Dr. Coleman wakes up in Anna's body, as Lindsey Lohan exits her room her bedroom door is still removed, but a few seconds after she runs out of the room after Harry the door has been re-attached.
Continuity mistake: When Anna and her Mom are first together in their switched states: "Anna" is trying to wake up "Mom" and on the wall, left to the bed, we see this ugly turtle wall ornament. In all shots subsequent, however, it's disappeared.
Continuity mistake: The 1st scene where Harry blows a horn in Anna's ear, she chased him out of the room and her blanket was thrown over on the RIGHT SIDE, but if you look close when she goes to close the door the blanket it almost all the way off the bed on the LEFT SIDE
Continuity mistake: When Anna (Tess) is in Anna's room in her robe with her hair up, she is looking for the fortune in Anna's pants pocket. She finds it and drops the pants, but in the next shot they show a close up of the fortune and Anna still has the pants in her hand.
Continuity mistake: When "Pink Slip" are singing "Ultimate" right at the end, you can see a small group of girls clumped together behind Anna and her girlfriends, and in the next shot they are completely gone. It's impossible for them to have moved entirely out of eyesight in those few seconds they are off camera.
Continuity mistake: When Anna and Tess are on the staircase checking to see if the coast is clear, we see Harry and Grandpa eating cereal, where Harry's cereal box is seen from the back. In the next shot of them, it's seen from the front.
Character mistake: When Anna and Tess go back to the Chinese restaurant to ask them about the fortune, Pei Pei calls her mother to them. When her mother responds to one question you can hear her talking but her mouth is no longer moving.
Continuity mistake: Anna's friend, the lead singer in the House of Blues performance, had not very much blush on, but an overload of eyeshadow on at the rehearsal, but when she got to the House of Blues she had an overload of both. When they were actually playing and after, the blush was cut back on again.
Audio problem: When the band Pink Slip is performing their song at The House of Blues, near the beginning of the song, Anna's two band mates are looking at her and wondering why she isn't playing. Maddie (the lead singer) is looking at Anna and singing, but Peg (the other guitar player) is looking at Anna and not singing. However, in the song, you can hear someone singing a harmony note opposite the main melody. How could that happen if Peg wasn't singing?
Revealing mistake: When Stacy Hinkhouse pulls the shirt over Anna/Tess, put it in slow motion and at one point you can see it is a stunt double and not Lindsay Lohan.
Continuity mistake: After Anna gets out of her second detention, when the things fall out of her bag, first you can see that the bag is still on her shoulder but her bag just turned upside down. In the next shot when you see all the things on the ground, you can see the bag touching the ground. When the shot goes back to Anna you can see the bag is on her shoulder again and upside down again.
Continuity mistake: When Tess is cutting the underwear off of Harry's head, she leaves the scissors on the counter away from the pile of the pieces of the underwear. Later you can see that it is in the pile of underwear.
Continuity mistake: When Tess comes in after work, there is a crisscross decoration on the wall far from the door, and there is something else next to the door. When she comes in after being out with Jake, the crisscross is directly next to the door.