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: 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. (00:01:35)
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: Right after Anna and Tess leave House of Chang, Tess' organizer goes off reminding her about a parent/teacher meeting. "Tess" freaks out, and "Anna" puts her hands on "Tess'" face to calm her down. The organizer has disappeared.
Continuity mistake: When Anna is pulling Tess in her bed she loses her grip and falls to the floor. As Anna falls you can see her bare foot come up, but in the previous shot she was wearing socks. (00:25:15)
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: Once Grandpa takes the underwear off Harry's head and sets it on the counter, it continually moves. Originally it is at the edge, draped over a little bit. Next it moves inward a little. After Mom shuts off the power, it is almost halfway on the counter. (00:11:40 - 00:13:00)
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 "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. (00:27:50)
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.
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: The way Tess holds the notepad, to show grandpa the message, changes between the shots. (00:11:30)
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. (00:11:25)
Continuity mistake: When Anna is arguing with her mom in the kitchen, she mentions Jake. When she does her entire body position changes completely between the instant camera cuts. (00:16:30)
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.
Continuity mistake: Jake's solepatch is extremely noticeable for most of the movie, and at the wedding, it is still there, but you can barely tell. It is noticeable that she shaved a great deal of it off before the wedding, which in real life would not happen.
Continuity mistake: When they find out that they have changed bodies, Tess (Anna's body) has a strand of hair going backwards over the back of her head in the shots from behind her, then when the shot faces her, all of her hair is straight down beside her face.
Continuity mistake: When Tess and Anna (in each other's bodies) go to the Chinese restaurant to get switched back, Pei Pei says, "No, you get back here" to her mother and she has a serious look on her face. When the shot changes, she is suddenly smiling very widely at Tess and Anna.
Continuity mistake: When Anna (Tess) wakes up and realizes she is in her daughter's body, Harry comes in and says that mom is dead. She goes into her room and sends Harry down stairs and she says he could eat her (Anna's) cereal. Harry goes down stairs and when Anna (Tess) is going to try to wake her up she reaches with two fingers to poke her and in the next shot she only poked her with one finger.
Answer: You need to think back to the poem... "A journey soon begins, its prize reflected in another's eyes. When what you see is what you lack, then selfless love will change you back." It says a journey SOON begins, not immediately, and it says "WHEN what you see...change you back". Basically the switch happens SOON, the switch back happens IMMEDIATELY.