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.
Continuity mistake: When Anna and her mum are at the rehearsal dinner, Jamie Lee Curtis (in Anna's body) cries. In the first shot, her first tear has rolled down to her lip, but in the next, it is around the same level as her nose.
Continuity mistake: While in class, when a student responds about Hamlet, Anna has her right arm raised. A shot later it's lowered.
Answer: Drummer: "what are you doing?" Anna/Tess: "I don't know, it's not working." Drummer: "Just do it".