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: When Pei Pei calls for her mother, she comes from the kitchen. She sees Anna and Tess and tries to escape by going back through the door she came from, but when the camera cuts back to her, she is about to enter the other door. (00:49:48)
Continuity mistake: At the wedding rehearsal, when they have just returned to their own bodies, Anna picks up a glass of water to toast but once she raises it, they feature a shot from behind her in which the glass and the liquid in it has completely changed. (01:26:36)
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".